CBSE Class 10 Science Short Answer Questions

• Chapter 1 Chemical Reactions And Equations
• Chapter 2 Acids, Bases And Salts
• Chapter 3 Metals And Non-Metals
• Chapter 4 Carbon And Its Compounds
• Chapter 5 Periodic Classification Of Elements
• Chapter 6 Life Processes
• Chapter 7 Control and Coordination
• Chapter 8 How do Organisms Reproduce

• Chapter 9 Heredity And Evolution
• Chapter 10 Light-Reflection 10 And Refraction
• Chapter 11 Human Eye And Colourful World
• Chapter 12 Electricity
• Chapter 13 Magnetic Effects Of Electric Current
• Chapter 14 Sources Of Energy
• Chapter 15 Our Environment
• Chapter 16 Management Of Natural Resources

Human Eye And Colourful World Short Answer Questions

Question 1. A star appears slightly higher than its actual position in the sky. Explain it.
Answer: It is due to atmospheric refraction. When the light of a star enters into the atmosphere, it is refracted continuously. The higher level of air acts as a rarer medium while the dense air near the surface of the earth acts as a denser medium. So, the atmosphere bends the starlight towards the normal.

As a result, the apparent position of stars is slightly different from its actual position. Thus the star appears slightly higher than its actual position in the sky.

Question 2. When we place a glass prism in the path of a narrow beam of white light, a spectrum is obtained. What happens when a second identical prism is placed in an inverted position to the first prism? Draw a labelled ray diagram to illustrate it.

The second prism recombines the spectrum obtained by the first prism. So from the other side of the second prism, n beam of white light is again obtained.

Question 3. With the help of scattering of light, explain the reason for the difference in colours ofthe sun as it appears during sunrise/sunset and noon.
Answer: The sun appears reddish at sunrise as well as at sunset and appears white at noon when it is overhead.

At sunrise/sunset, the blue light of shorter wavelength gets scattered away while passing through the thicker layer of air/large distance through air and red light of longer wavelength reaches our eye.

At noon, the sun is overhead and the light of the sun travels a relatively shorter distance to our eyes little blue and violet colours are scattered, and white light reaches our eyes.

Question 4. Why do some people use bifocal lenses?
Answer: Some people suffer from both myopia and hypermetropia. Such people require bi-focal lenses. The upper part ofthe bi-focal lens is a concave lens used for distant vision while its lower part is a convex lens used for reading purposes. These days, refractive defects are also corrected by using contact lenses or through surgical interventions.

Question 5. What is the “power of accommodation ofthe eye”? What happens to the image distance when the object being viewed is moved away from the eye?
Answer: The power of accommodation of the eye is the ability of the eye lens to adjust its focal length to see nearby and distant objects.

Image distance in the eye is fixed, being equal to the distance of the retina from the eye lens.

Question 6. Why do we observe the seven colours when white light passes through a glass prism? Which component of white light deviates the least?
Answer: When light passes through a prism offers different refractive indices to the different wavelengths of light. Thus, each colour suffers a different deviation. The red light deviates the least.

Question 7. Calculate the maximum power of accommodation of a person having normal vision.

A person needs to use glasses to read a newspaper. Identify the defect in her vision and the type oflens she would need to correct it.

Sometimes when we enter into a dark room from bright sunlight we are unable to see objects. Why?

Answer: D = 25 cm, Now, P = 1/f- D = 100/D = 100/25 = 4 D, thus for a person having normal vision, the power of accommodation is about 4 dioptre.

Long-sightedness, a convex lens.

The pupil regulates and controls the amount of light entering the eye. In bright sunlight, the size ofthe pupil is small and when we enter a dark room it takes some time for the pupil to expand in size due to dim light.

Question 8. A person can see up to 3 metres only. Prescribe a lens for him so that he can see up to 12 metres.
Answer: Clearly, the lens used in this case should be such that the rays proceeding from a point distant 12 m from the eye should, after refraction, appear to come from a point distant 3 m from the eye. Here, u =- 12 m, v =- 3 m, /= ?

Using lens formula, \(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\)

⇒ \(\begin{aligned}
& =-\frac{1}{3}+\frac{1}{12} \\
& =-\frac{1}{4} \quad \text { or } f=-4 \mathrm{~m}
\end{aligned}\)

Thus, a concave lens of a focal length of 4 m should be used.

Question 9. A narrow beam PQ of white light is passing through a glass prism ABC as shown in the diagram.

1. Trace it on your answer sheet and show the path of the emergent beam as observed on the screen DE.
2. Write the name and cause ofthe phenomenon observed.
3. Where else in nature is this phenomenon observed?
4. Based on this observation, state the conclusion which can be drawn about the constituents of white light.

Answer: The diagram is shown below

The phenomenon is called the dispersion of light. It is because ofthe reason that different wavelengths oflight travel at different speeds in the glass prism. In a rainbow. White light consists of seven different wavelengths viz. violet, indigo, blue, green, yellow, orange and red.

Question 10. A person with a myopic eye cannot see objects beyond a distance of 1.5 m. What would be the power ofthe corrective lens used to restore proper vision?
Answer: The remedial lens should make the object at infinity appear at the far point.

1. For an object at infinity, u =-∞
2. Far point distance of the defective eye, v =- 150 cm
3. By lens formula,

⇒ \(\begin{aligned}
\frac{1}{f} & =\frac{1}{v}-\frac{1}{u} \\
& =\frac{1}{-150}-\frac{1}{-\infty} \\
& =-\frac{1}{150}+0
\end{aligned}\)

⇒ \(=-\frac{1}{150}\)

or, f=-150cm.

Power, \(\mathrm{P}=\frac{1}{f(\text { in } \mathrm{m})}\)

A negative sign shows that the remedial lens is concave.

Question 11. Why do we have two eyes for vision and not just one?
Answer: Advantage of binocular vision: There are many advantages of having two eyes instead of one. These are as follows.

1. It gives a wider horizontal field of view of about 180°.
2. It helps to detect even fainter objects.
3. It provides a three-dimensional effect of objects around us.
4. The two eyes give relief to each other after every fraction of a second.

Question 12. A person is unable to read a book clearly when kept at a distance of 25 cm from his eye. Name the defect. How can it be corrected? Draw ray diagrams for defective eye-corrected eyes and explain them.
Answer: Hypermetropia or long-sightedness.

It is corrected by using a convex lens of suitable focal length. The diagrams are as shown below:

Defective eye: Rays from the object at N are focused beyond the retina i.e., near point goes away from the eye.

Corrected eye: Using a converging lens makes the image at the retina.

Question 13. Explain why the colour of the clear sky is blue.
Answer: The molecules of air and other fine particles in the atmosphere have a size smaller than the wavelength of visible light.

These are more effective in scattering light of shorter wavelength at the blue end than light of longer wavelength at the red end. The red light has a wavelength about 1.8 times greater than that of blue light.

Thus, when sunlight passes through the atmosphere, the fine particles in the air scatter the blue colour (shorter wavelength) more strongly than red. The scattered blue light enters our eyes. If the earth had no atmosphere, there would not have been any scattering.

Question 14. State the cause of dispersion, when white light enters a glass prism. Explain with a diagram.
Answer: Light is made up of different colours. Each colour travels at its speed inside a prism. Due to this, different light colours bend through different angles for the incident ray, as they pass through a prism. The red light bends the least while the violet the most.

Thus, the rays of each colour emerge along different paths and thus become distinct. It is the band of distinct colours that we see in a spectrum. The diagram is as shown.

A beam of white light falling on a glass prism gets split up into seven colours marked 7 as shown in the diagram:

The colours at positions marked 3 and 5 are similar to the colour ofthe sky and the colour of gold metal respectively. Is the above statement made by the Is student correct or incorrect Justify?

Which of the above-shown positions corresponds approximately to the colour of:

1. A Brinjal
2. Danger Signal
3. Neel Which Is Applied To The Clothes
4. Orange

Answer: As a result of dispersion produced by the prism, the white light is split up into seven colours. These colours as we know are represented by the letters of the word ‘VIBGYOR’.

Thus, blue is in the 3rd position and yellow is in the 5th position. These are the colours of the sky and the gold medal respectively. Thus, the statement is correct.

The positions of the colours ofthe given objects are represented by:

1. brinjal ……….7
2. Danger singal…….1
3. Neel ……….6
4. Organe……2

Question 15. A person wears glasses of power -2.5 D. Is the person far-sighted or near-sighted? What is the point of the person without glasses?
Answer: P =- 2.5 D.

Negative power shows that the lens is concave, so the person is near-sighted.

⇒ \(\begin{aligned}
f & =\frac{1}{\mathrm{P}} \\
& =\frac{1}{-2.5} \mathrm{~m}=-\frac{2}{5} \mathrm{~m} \\
& =-40 \mathrm{~cm} \\
u & =-\infty, v=?
\end{aligned}\)

From the lens formula,

⇒ \(\frac{1}{v}=\frac{1}{f}+\frac{1}{u}=\frac{1}{-40}+\frac{1}{-\infty}=\frac{1}{-40}-0=-\frac{1}{40}\)

v=-40 cm

Thus, the far point of the eye is 40 cm from the eye.

Question 16. List two causes leading to myopia of the eye. Draw ray diagrams to show the image formation in case of defective eye and correct eye.
Answer: The two main causes of myopia are:

1. The eyeball is longer than normal.
2. Decrease in the focal length of the eye lens

Question 17. A person needs a lens of power -2.5 dioptres for correcting his vision. Name the defect of vision he is suffering from. Which lens will he be using for the correction1? Also, find the focal length oflens.
Answer: The person is using a concave lens of power -2.5 D. The person is, therefore, suffering from myopia. He is using a concave lens for the correction of the eye. Since P =1If, therefore, f= 1/P = 1/2.5 = 0.4 m = 40 cm.

Question 18. Explain how a normal human eye can see distinctly the object placed at a distance as well as those placed at a nearer distance. What are the far point and near point of a normal human eye?
Answer: For seeing distant objects, the focal length ofthe eye lens should be large and for seeing near objects the focal length of the eye lens should be small.

The focal length of the eye lens can be adjusted with the help of ciliary muscles holding the lens in position. The far point and near point are at infinity and 25 cm respectively.

Question 19. Name the part of the eye where the image is formed by the eye lens. What is the nature ofthe image formed? How is this image sent to the brain?
Answer: The image of the object formed by the eye lens is at the retina of the eye. The image formed on the retina is real and inverted. The image is sent to the brain with the help of the optic nerve.

Question 20. An old person is unable to see nearby objects as well as distant objects, What defect of vision is he suffering from? What kind oflens will be required to see the nearby as well as distant objects? Give reasons.
Answer: Presbyopia.

He shall have to use both kinds of lenses, convex lens for long-sightedness and concave lens for short-sightedness.

Question 21. Why does the sun appear reddish early in the morning? Illustrate with the help of a labelled diagram.
Answer: It is due to the scattering of light. The light near the horizon passes thicker layers of air and a larger distance of the atmosphere; hence, most ofthe blue light is scattered away and longer wavelength reaches our eyes giving rise to the reddish colour of the sun.

Question 22. Why does it take some time to see the objects in a dim room when we enter the room from the bright sunlight outside?
Answer: In bright light, the size ofthe pupil is small to control the amount of light entering the eye. When we enter a dim room, it takes some time so that the pupil to expand and allow more light to enter and help to see things.

Question 23. Why does it take some time to see objects in a cinema hall when we just enter the hall from, bright sunlight? Explain in brief
Answer: The pupil regulates and controls the amount oflight entering the eye. In bright sunlight, the size of the pupil is small and when we enter the cinema hall takes some time for the pupil to expand in size due to dim light.

Question 24. Describe the formation of the rainbow in the sky.
Answer: A rainbow is always formed in a direction opposite to that of the sun. The water droplets act like small prisms. They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop. Due to the dispersion oflight and internal deflection, different colours reach the observer’s eye.

1. What is meant by the least distance of distinct vision?
2. How does the thickness ofthe eye lens change when we shift looking from a distant tree
   to reading a book?

Answer: It is the minimum distance, to which normal eyes can see two similar objects distinctly.

The eye lens is comparatively thicker while reading a book.

Question 25. To correct distant vision, a person needs a lens of power -5.5 dioptres, and to correct near vision, he needs a lens of power +1.5 dioptres. What is the focal length of the lens required for correcting distant vision and near vision?

Answer: Power of distance viewing part of the lens,

P₁ =-5.5 D

The focal length of this part

⇒ \(f_1=\frac{1}{P_1}=\frac{1}{-5.5} \mathrm{~m}\)

= -18.73 cm.

As the power of the near-vision part is measured relative to the main part of the lens of power – 5.5 D, so we use

P₁ + P₂ = P

or — 5.5 + P₂ = + 1.5

or P₂ = + 6.5 D

Focal length near-vision part

⇒ \(\begin{aligned}
f_2 & =\frac{1}{\mathrm{P}_2}=\frac{1}{+6.5} \mathrm{~m} \\
& =+15.4 \mathrm{~cm}
\end{aligned}\)

Question 26. The far point of a myopic person is 80 cm in front of the eye. What is the nature and power ofthe lens required to correct the problem1
Answer: The remedial lens should make the objects at infinity appear at the far point.

∴ For an object at infinity u =-∞

Far point distance of the defective eye, v =- 80 cm

By lens formula, \(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}=\frac{1}{-80}-\frac{1}{-\infty}=-\frac{1}{80}+0=-\frac{1}{80}\)

or f=-80cm

Power, \(\mathrm{P}=\frac{100}{f(\mathrm{in} \mathrm{cm})}\)

⇒ \(\begin{aligned}
& P=\frac{100}{-80} \\
& P=-1.25 D
\end{aligned}\)

A negative sign shows that the remedial lens is concave.

Question 27. Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point ofthe normal eye is 25 cm.
Answer: The object placed at 25 cm from the correcting lens must produce a virtual image at 1 m or 100 cm.

u = -25 cm, v =- 100 cm

By lens formula \(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}=\frac{1}{-100}-\frac{1}{-25}=-\frac{1}{100}+\frac{1}{25}=+\frac{3}{100}\)

or \(f=+\frac{100}{3} \mathrm{~cm}=+\frac{1}{3} \mathrm{~m}\)

Power, \(\mathrm{P}=\frac{1}{f}=+\frac{3}{1}=+3 \mathrm{D}\)

Question 28. Why is a normal eye not able to see the objects placed closer than 25 cm?
Answer: At a distance of less than 25 cm, the ciliary muscles cannot bulge the eye lens anymore, the object cannot be focussed on the retina and it appears blurred to the eye, as shown in the figure.

Object O within 25 cm from the eye is not focused on the retina and is seen blurred.

Question 29. What happens to the image distance in the eye when we increase the distance of an object from the eye?
Answer: Due to its property of accommodation, the eye lens of a normal eye forms images of objects at various distances on the same retina. So the image distance in the eye remains the same.

Question 30. Why do stars twinkle?
Answer: The apparent position of a star is slightly different from the actual position due to the refraction of starlight by the atmosphere. Due to the variation in the atmospheric conditions, the amount oflight from a particular star changes randomly with time. This gives rise to a twinkling effect of the star.

Question 31. Explain why the planets do not twinkle.
Answer: As the planets are much closer to the Earth, the amount oflight received from them is much greater and the fluctuations caused in the amount of light due to atmospheric refraction are negligible as compared to the amount oflight received from them.

Question 32. Why does the sun appear reddish early in the morning?
Answer: Early in the morning, the sun is near the horizon. Sunlight reaches us after covering a large thickness ofthe atmosphere.

So shorter waves of blue region are almost completely scattered away by the air molecules. Red waves of longer wavelength are least scattered and reach our eyes. The sun appears red.

Question 33. Why does the sky appear dark instead of blue to an astronaut?
Answer: The atmosphere is quite thin at very high altitudes. There is almost no scattering of sunlight. So the sky appears dark to an astronaut.

Question 34. What is meant by the power of accommodation of the eye?
Answer: The power of accommodation of the eye is the maximum variation of its power for focusing on near and far (distant) objects. for a normal eye, the power of accommodation is about four diopters.

Question 35. A student sitting at the back of the classroom cannot read the letters written on the blackboard. What advice will a doctor give to her? Draw a ray diagram for the correction ofthis defect.
Answer: The student is suffering from myopia or near-sightedness. In myopia, one can see nearby objects clearly but cannot see distant objects distinctly. The doctor advises a concave lens of suitable power to bring the image back into the retina.

The ray diagram for the correction of this defect is shown below

Question 36. A person needs a lens of power -4.5D for correction of her vision.

1. What kind of defect in vision is she suffering from?
2. What is the focal length ofthe corrective lens?
3. What is the nature ofthe corrective lens?

Answer: As the power of the lens is negative, she must be suffering from myopia.

Power, P =- 4.50, focal length, f=?

⇒ \(\mathrm{P}=\frac{1}{f} \Rightarrow f=\frac{1}{\mathrm{P}}=\frac{1}{-4.5}=-0.222 \mathrm{~m}=-22.2 \mathrm{~cm}\)

The nature ofthe corrective lens is concave or divergent.

Question 37. How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out ofthe second prism as white light? Draw the diagram.
Answer: A narrow beam of white light incident on one prism emerges out of the identical prism placed in an inverted position to the first prism close to the first prism as shown in the figure given below.

Question 38. Draw a ray diagram showing the dispersion through a prism when a narrow beam of white light is incident on one of its refracting surfaces. Also, indicate the order of the colours ofthe spectrum obtained.
Answer:

Question 39. Why do we see a rainbow in the sky only after rainfall?
Answer: We see a rainbow in the sky only after rainfall due to the dispersion of sunlight by tiny water droplets, present in the atmosphere due to rainfall. The water droplets act as a prism.

They refract and disperse the incident sunlight then reflect it internally and finally refract it again when it comes out of a raindrop hence due to the dispersion of light and internal reflection, rainbow formation takes place during rainfall.

Question 40. Why is the colour ofthe clear sky blue?
Answer: The blue colour of the clear sky is due to Rayleigh’s scattering of sunlight. The molecules of air and other fine particles in the atmosphere have sizes smaller than the wavelength of visible light.

These are more effective in scattering light of shorter wavelengths at the blue end than light of longer wavelengths at the red end.

Question 41. What is the difference in colours of the sun observed during sunrise-sunset and noon? Explain each.
Answer: During sunrise/sunset, the sun looks reddish because, at this stage, rays from the sun have to travel a much larger part of the atmosphere. The red colour having the largest wavelength is scattered the least.

At noon, the sun is nearly overhead. The sunlight has to pass through a smaller portion of the earth’s atmosphere. the scattering is much less and hence the sun looks White.

Question 42. A child sitting in a classroom is not able to read the writing on the blackboard.

1. Name the type of defect from which his eye is suffering.
2. With the help of a ray diagram show how this defect can be remedied.

Answer: The child’s eye is suffering from the defect of myopia.

The defect can be removed by using a concave lens as shown in the figure below:

Question 43. Why do we have two eyes instead of one?
Answer: Two eyes are better than one eye because of the following reasons:

• The field of view with two eyes is more than with one eye.
• Two eyes give three three-dimensional pictures of an object whereas one eye gives only two dimensional picture of an object.

Human Eye And Colourful World Multiple Choice Questions

Question 1. The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to

1. Presbyopia.
2. Accommodation.
3. Near-Sightedness.
4. Far-Sightedness.

Answer: 2. The ability of the eye to focus objects at different distances is called accommodation.

Question 2. The human eye forms the image of an object in its

1. Cornea.
2. Iris.
3. Pupil.
4. Retina.

Answer: 4. The human forms the image of an object at its retina.

Question 3. The least distance of distinct vision for a young adult with normal vision is about

1. 25 m.
2. 2.5 cm.
3. 25 cm.
4. 2.5 m.

Answer: 3. The least distance of distinct vision for a normal eye is 25 cm.

Question 4. The change in focal length of an eye lens is caused by the action of the

1. Pupil.
2. Retina.
3. Ciliary Muscles.
4. Iris.

Answer: 3. The change in the focal length of the eye is due to the action of ciliary muscles.

Question 5. A person cannot see distinct objects kept beyond 2m. This defect can be corrected by using a lens of power

1. + 0.5D
2. – 0.5 D
3. + 0.2 D
4. – 0.2 D

Answer: 2. – 0.5 D

Question 6. A student sitting on the last bench can read the letters written on the blackboard but is not able to read the letters written in his textbook. Which of the following statements is correct?

1. The near point of his eyes has receded away
2. The near point of his eyes has come closer to him
3. The far point of his eyes has come closer to him
4. The far point of his eyes has receded away

Answer: 1. The near point of his eyes has receded away

Question 7. A prism ABC (with BC as the base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in the figure. In which of the following cases, after dispersion, the third colour from the top corresponds to the colour of the sky?

1. 1
2. 2
3. 3
4. 4

Answer: 2. 1

Question 8. At noon the sun appears white as

1. Light Is Least Scattered
2. All The Colours of white Light Are Scattered Away
3. Blue Colour Is Scattered The Most
4. Red Colour Is Scattered The Most

Answer: 1. Light Is Least Scattered

Question 9. Which of the following phenomena of light are involved in the formation of the rainbow?

1. Reflection, Refraction And Dispersion
2. Refraction, Dispersion And Total Internal Reflection
3. Refraction, Dispersion And Internal Reflection
4. Dispersion, scattering and total internal reflection

Answer: 3. Refraction, Dispersion And Internal Reflection

Question 10. The twinkling of stars is due to atmospheric

1. Dispersion Of light By Water Droplets
2. Refraction Of Light By Different Layers Ofvarying Refractive Indices
3. Scattering Of light By Dust Particles
4. Internal Reflection of Light By Clouds

Answer: 2. Refraction Of light By Different Layers Ofvarying Refractive Indices

Question 11. The clear sky appears blue because

1. Blue Light Gets Absorbed In The Atmosphere
2. Ultraviolet Radiations Are Absorbed In The Atmosphere
3. Violet And Blue Lights Get Scattered More Than Lights Of All Other Colours By The
   Atmosphere
4. Light all other Colours Is Scattered More Than The Violet And Blue Colourlights By The Atmosphere

Answer: 3. Violet And Blue Lights Get Scattered More Than Lights Of All Other Colours By The Atmosphere

Question 12. Which of the following statements is correct regarding the-propagation oflight of different colours of white light in the air?

1. Red Light Moves the Fastest
2. Blue Light Moves Faster Than Green Light
3. All The Colours of white Light Move at the Same Speed
4. Yellow Light Moves With The Mean Speed As That Ofthe Red And The Violet Light

Answer: 3. All The Colours of white Light Move With The Same Speed

Question 13. The danger signals installed at the top of tall buildings are red. These can be easily seen from a distance because among all other colours, the red light

1. Is Scattered The Most By Smoke Or Fog
2. Is Scattered The Least By Smoke Or Fog
3. Is Absorbed The Most By Smoke Or Fog
4. Moves Fastest In Air

Answer: 2. Is Scattered The Least By Smoke Or Fog

Question 14. Which of the following phenomena Contributes Significantly To The Reddish Appearance Of The Sun At Sunrise Or Sunset?

1. Dispersion Of light
2. Total Internal Reflection Of light
3. Scattering Of light
4. Reflection Of Light From The Earth

Answer: 2. Total Internal Reflection Oflight

Question 15. The Bluish Colour Of Water In Deep Sea Is Due To

1. The Presence Of algae And other plants Found In Water
2. Reflection Ofsky In Water
3. Scattering Oflight
4. Absorption Oflight By The Sea

Answer: 3. Scattering Of light

Question 16. When Light Rays Enter The Eye, Most of the refraction Occurs At The

1. Crystalline Lens
2. Outer Surface Of the Cornea
3. Iris
4. Pupil

Answer: 2. Outer Surface Of the Cornea

Question 17. The Focal Length Of The Eye Lens Increases When Eye Muscles

1. Are Relaxed And Lens Becomes Thinner
2. Contract And Lens Becomes Thicker
3. Are Relaxed And Lens Becomes Thicker
4. Contract And Lens Becomes Thinner

Answer: 1. Are Relaxed And Lens Becomes Thinner

Question 18. Which of the following Statements Is Correct?

1. A Person With Myopia Can See Distant Objects Clearly
2. A Person With Hypermetropia Can See Nearby Objects Clearly
3. A Person With Myopia Can See Nearby Objects Clearly
4. A Person With Hypermetropia Cannot See Distant Objects Clearly

Answer: 3. A Person With Myopia Can See Nearby Objects Clearly

Question 19. Tarun’s father is an eye surgeon. He persuaded his father to put a camp in his society to educate people about eye donation. Rohan made a banner. One donation can give eyevision to two blind persons.

1. Name the part of the eye that is used, during eye transplant.
2. Name the defect that can be corrected by this transplant.
3. What value of Tarun is reflected?
4. The defect is caused by to cornea.

Answer: 1. Cornea.

1. A defect is caused by to cornea.
2. Tarun shows sympathy, compassion and empathy in his behaviour.

Chapter 12 Electricity Short Questions And Answers

Question 1. Redraw the circuit question 1, putting in an ammeter to measure the current through the resistors and a voltmeter to measure the potential difference across the 12Ω resistor. What would be the readings in the ammeter and the voltmeter?
Answer: The required circuit diagram is given below

Reading of ammeter, \(I=\frac{V}{R}\)
⇒ \(=\frac{6}{25}\)
= 0.24A

Reading of voltmeter V=I.R
0.24×12
= 2.88 v

Question 2. Judge the equivalent resistance when the following are connected:

1. Inland 106£l,
2. 1 £l and 103£l, and 106£l.

Answer: When the resistors are connected in parallel, the equivalent resistance is smaller than the smallest individual resistance.

Equivalent resistance < 1Ω.

Equivalent resistance <1Ω.

Read and Learn More CBSE Class 10 Science Short Answer Questions

Question 3. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
Answer: The advantages of connecting electrical devices in parallel with the battery are as follows:

Each device gets the full battery voltage. The parallel circuit divides the current through the electrical devices. Each device gets proper current depending on its resistance. If one device is switched OFF/ON, others are not affected.

Question 4. Why does the 1 cord of an electric heater not glow while the heating element does?
Answer: Both the cord and the heating element ofan electric heater carry the same current. However, the heating element becomes hot due to its high resistance (H = I2Rf) and begins to glow. The cord remains cold due to its low resistance and does not glow.

Question 5. Compute the heat generated while transferring 96,000 coulombs of charge in one hour through a potential difference of 50 V.
Answer: Here, Q = 96,000 C, t = 1 hour = 3600 s, V = 50 V

The heat generated, H = VQ

H = 50 V x 96,000 C

H = 48,00,000 J.

Question 6. An electric iron of resistance 20H takes a current of 5 A. Calculate the heat developed in 30 seconds.
Answer: Here, R = 20 Q, 1 = 5 A, t = 3 s

Heat developed is

H= I2Rt

H=25x20x30

H=15000 J.

Question 7. An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2h.
Answer:

Here, I = 5 A. V = 220 V, / = 2 h = 7200 s

Power, P = VI

=220×5

=1100W

Energy consumed = px

= 100wx7200s

=7,20,000J.

Question 8. Compare the power used in the 2Ω resistor in each of the following circuits: 1. a 6 V battery in series with 1Ω and 2 Ω resistors, and a 4 V battery in parallel with 12 Ω and 2Ω resistors.
Answer: The circuit diagram is shown in the figure

Total resistance R=1+2=3

Potential difference v=6v

Current \(\mathrm{I}=\frac{\mathrm{V}}{\mathrm{R}}=\frac{6 \mathrm{~V}}{3 \Omega}=2 \mathrm{~A}\)

Power used in 2Ω resistor = I2R= (2)2×2=8w.

The circuit diagram for this case is shown below:

Power used in 2Ω1 resistor \(\begin{aligned}
& =\frac{V^2}{R}=\frac{(4)^2}{2} \\
& =8 \mathrm{~W}
\end{aligned}\)

=8w

Question 9. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to the electric mains supply. What current is drawn from the line if the supply voltage is 220 V?
Answer: Total power consumed in the circuit = 100 + 60 = 160 W

voltage v=220

power =vI

Current \(I=\frac{\text { Power }}{V}\)

⇒ \(\begin{aligned}
& =\frac{160}{220} \\
& =0.727 \mathrm{~A} .
\end{aligned}\)

=0.727A

Question 10. Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?
Answer: Energy used by 250 W TV set in 1 hour

= 250 W x 1 h = 250 Wh

Energy used by 1200 W toaster in 10 minutes.

= 1200 W x 12 min.

⇒ \(=1200 \mathrm{~W} \times \frac{12}{60} h\)

= 240 Wh

Thus, the TV set uses more energy than the toaster.

Question 11. An electric heater of resistance 8 Q draws 15 A from the service mains for 2 hours. Calculate the rate at which heat is developed in the heater.
Answer: Here, R = 8 £2,I = 15A, t = 2h

The rate at which heat is developed in the heater is equal to the power

Therefore \(\begin{aligned}
\mathrm{P} & =\mathrm{I}^2 \mathrm{R}=(15)^2 \times 8 \\
& =\mathbf{1 8 0 0} \mathbf{J s}^{-1}
\end{aligned}\)

Question 12. Explain why a conductor offers resistance to the flow of current. Differentiate between conductor, resistor, and resistance.
Answer: We know that the motion of electrons in an electric circuit constitutes an electric current. However, the electrons are not completely free to move within the conductor. They are restrained by the attraction of the atoms among which they move.

Conductor: Any substance that is capable of readily transmitting heat, electricity, etc., is called a conductor.

Resistor: A conductor having some appreciable resistance is called a resistor.

Resistance: It is the property of a material by which it opposes the flow of current through it.

2. A piece of wire of resistance 6Q is connected to a battery of12 V. Find the amount of current flowing through it. Now, the same wire is redrawn by stretching it to double its length. Find the resistance of the new (redrawn) wire.
Answer: Here, resistance (R) = 6 Q, potential difference (V) = 12 V

V=IR

Or \(I=\frac{V}{R}=\frac{12 \mathrm{~V}}{6 \Omega}=2 \mathrm{~A}\)

Original Resistance

⇒ \(\mathrm{R}=\rho \frac{l}{\mathrm{~A}}\)

If the wire is doubled, then its new lengthl’ = 21 and new area of cross-section \(\mathrm{A}^{\prime}=\frac{\mathrm{A}}{2} \text {. }\)

The New Resistance

⇒ \(\mathrm{R}^{\prime}=\rho \frac{l^{\prime}}{\mathrm{A}^{\prime}}=\rho \frac{2 l}{\frac{\mathrm{A}}{2}}=\frac{4 \rho l}{\mathrm{~A}}=4 \mathrm{R}\)

or R’ = 4R, i.e., the resistance increases to four times

Question 13. Mention the condition under which charges can move in a conductor. Name the device which is used to maintain this condition in an electric circuit.
Answer: Charges can move, if there is a potential difference across the two ends ofthe conductor. An electric cell or a battery consisting of one or more cells can maintain an electric current in an electric circuit.

Question 14. Define the term ‘volt’. State the relation between work, charge, and potential difference for an electric circuit. Calculate the potential difference between the two terminals of a battery, if100joules ofwork is required to transfer 20 coulombs of charge from one terminal ofthe battery to the other.
Answer: One-volt potential difference between two points in a current-carrying conductor when 1 joule of work is done to move a charge of coulomb from one point to the other.

The relation is V = W/Q

Given, W = 100 J, Q = 20, V = ?

Using the relation, V = W/Q, we have

V = 100/20 = 5 V

Question 15. (a) How is the direction of electric current related to the direction of flow of electrons in a wire? Calculate the current in a circuit, if 500 C of charge passes through it in 10 minutes.
Answer: The direction of electric current is opposite to the direction of flow of electrons in a wire.

Given Q = 500 C,

t = 10 minute

= 10 x 60 = 600 s,I = ?

Using the relation, \(I=\frac{Q}{T}\)

= 500/600=083A

Question 16. Define electric current and state its SI unit. With the help of Ohm’s law explain the meaning of 1-ohm resistance.
Answer: It is defined as the rate of flow of electric charge through an electric circuit. Its SI unit is ampere (A). Ohm’s law is V = IR Let V = 1 ohm and1=1 ampere, then R = 1 volt/1 ampere =1 ohm Thus, 1 ohm is the resistance of a conductor, under the effect of a potential difference of volt across it a current of ampere flows through it.

Question 17. Find the current drawn from the battery by the network of four resistors

Answer: Equivalent resistance of the given network is

⇒ \(\frac{1}{\mathrm{R}}=\frac{1}{\mathrm{R}_4}+\frac{1}{\mathrm{R}_1+\mathrm{R}_2+\mathrm{R}_3}=\frac{1}{10}+\frac{1}{10+10+10}\)

⇒ \(=\frac{1}{10}+\frac{1}{30}=\frac{3+1}{30}=\frac{4}{30}\)

⇒ \(\mathrm{R}=\frac{30}{4}=7.5 \Omega\)

⇒ \(\begin{aligned}
& \mathrm{I}=\frac{\mathrm{V}}{\mathrm{R}}=\frac{3}{7.5}=\frac{30}{75}=\frac{2}{5} \\
& \mathrm{I}=0.4 \mathrm{~A}
\end{aligned}\)

Question 18. State the formula co-relating the electric current flowing in a conductor and the voltage applied across it. Also, show this relationship by drawing a graph. What would be the resistance of a conductor, if the current flowing through it is 0.35 ampere when the potential difference across it is 1.4 volts?
Answer: It states that Physical conditions remain the same the current flowing through the conductor is directly proportional to the potential applied across its two ends.”

The graph is shown below

Given V = 1.4 V,I = 0.35 A

Now, resistance is given by the expression

⇒ \(\mathrm{R}=\frac{\mathrm{V}}{\mathrm{I}}=\frac{1.4}{0.35}=4 \Omega\)

Question 19. The resistivity of two elements A and B are 1.62 x 10~8 Q m and 520 x  respectively. Out ofthese two, name the element that can be used to make:

1. The filament of the electric bulb.
2. Wires for electrical transmission lines. Justify your answer in each case.

Answer: Element B: It has more resistivity (520 x 10-8 £2 m).

Element A: It has less resistivity and hence less heating effect/dissipation of energy during transmission of power.

Question 20. Draw the nature of the V-Igraph for a nichrome wire (V – Potential difference, I – Current) A metallic wire of625 mm in length offers a 4 12 resistance. If the resistivity ofthe metal is 4.8 x IQ-7 ohm-meter, then calculate the area of the cross-section of The wire. 
Answer: The graph is as shown:

Given p = 4.8 x 10-7n m,

L = 625 mm = 0.625 m, R = 4 Q, A = ?

Using the expression \(\mathrm{R}=\frac{\rho \mathrm{L}}{\mathrm{A}}\) we have

⇒ \(A=\frac{\rho L}{R}\)

⇒ \(\begin{aligned}
& =\frac{4.8 \times 10^{-7} \times 0.625}{4} \\
& =0.75 \times 10^{-7} \mathrm{~m}^2
\end{aligned}\)

Question 21. Derive the relation R=R1+R2 + R3 when three resistors Rp R2 andR3 are connected in series in an electric circuit.
Answer: Consider three resistors of resistances, R1, R2, and R3 connected in series to a cell of potential V as shown in the figure. Since the three resistors are connected in series, therefore, the current through each of them is the same. By Ohm’s law

V1=iR1 V2=IR 2 V3=IR3

IfRs are the equivalent resistance ofthe series combination, then on applying a potential difference V across it, the same must flow through it.

Therefore,

V = IRS

v = v1 + v2 + v3

IRS = IR1 + IR2 + IR3

Rs = Rx + R2 + R3

Question 22. (a) Nichrome wire of length L and radius ‘R’ has a resistance of 10 Q. How would the resistance ofthe wire change when:

1. only the length ofthe wire is doubled.
2. only diameter ofthe wire is doubled1? Justify your answer.
3. Why are elements of electrical heating devices made made-up of alloys?

Answer:

R⇒ L

So resistance becomes two times,

i.e., R = 2 x 10 = 20 Q.

⇒ \(\mathrm{R} \propto \frac{1}{\mathrm{~A}} \propto \frac{1}{\mathrm{D}^2}\)

So when the diameter is doubled, resistance becomes \(\frac{1}{4}[latex] of its original

i.ec., R=10/4=2.5

This is because alloys do not oxidize readily at high temperatures.

Question 23. Draw schematic diagrams ofan electric circuit comprising of3 cells and an electric bulb, ammeter, and plug-key in the ON mode and another with the same components but with two bulbs in parallel and a voltmeter across the combination.
Answer:

Question 24. The wattage of a bulb is 24 W when it is connected to a 12 V battery. Calculate its effective wattage if it operates on a 6 V battery (Neglect the change in resistance due to unequal heating ofthe filament in the two cases).
Answer: Given: = 24 W, Vx = 12 V, P2 = ?, V2 = 6 V

Using [latex]\begin{aligned}
\mathrm{P} & =\frac{\mathrm{V}^2}{\mathrm{R}} \\
\frac{\mathrm{P}_1}{\mathrm{P}_2} & =\frac{\mathrm{V}_1^2}{\mathrm{~V}_2^2}
\end{aligned}\)

⇒ \(\begin{aligned}
\mathrm{P}_2 & =\left(\frac{\mathrm{V}_2}{\mathrm{~V}_1}\right) \times \mathrm{P}_1 \\
& =\left(\frac{6}{12}\right)^2 \times 24 \\
& =\frac{1}{4} \times 24 \\
& =6 \mathrm{~W}
\end{aligned}\)

Question 25. How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb is 1200 Q? If in place of the bulb, a heater of resistance 100 Q is connected to the sources, calculate the current drawn by it.
Answer: Given: V:220 V, Rx = 1200 £2,1, =?

R2 = 100 Q, I2 =?

Using OHm’s Law

⇒ \(\begin{aligned}
\mathrm{V} & =\mathrm{I}_1 \mathrm{R}_1 \\
\mathrm{I}_1 & =\frac{\mathrm{V}}{\mathrm{R}_1} \\
& =\frac{220}{1200} \\
& =0.18 \mathrm{~A}
\end{aligned}\)

And, \(\begin{aligned}
\mathrm{I}_2 & =\frac{\mathrm{V}}{\mathrm{R}_2} \\
& =\frac{220}{100} \\
& =2.2 \mathrm{~A}
\end{aligned}\)

Question 26. Out of the two wires X and Y shown below, which one has greater resistance? Justify your answer.
Answer: Wire ‘Has greater resistance as it has more length than wire It is because the resistance of wire is directly proportional to the length of wire for the same area of cross-section for the same material.

Question 27. An electric iron has a rating of 750 W, 220 V. Calculate the current flowing through it, and its resistance when in use.
Answer: Given: P = 750 W, V = 220 V

p=VI

750=220xI

⇒\(I=\frac{750}{220}=3.40 \mathrm{~A}\)

⇒\(\begin{aligned}
\mathrm{P}=\frac{\mathrm{V}^2}{\mathrm{R}} \Rightarrow \mathrm{R}=\frac{\mathrm{V}^2}{\mathrm{P}} & =\frac{220^2}{750} \\
& =64.53 \Omega
\end{aligned}\)

Question 28. Why is the parallel arrangement used in domestic wiring?
Answer: Parallel arrangement is used in domestic wiring because of the following:

All the appliances work at the same voltage as that of the electric supply.

If one ofthe appliances is out of order, e.g., if a bulb gets fused, all other appliances keep on working as the circuit is not broken in the parallel arrangement of devices.

Question 29. Let the resistance of an electrical component remain constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?
Answer: When the potential difference is halved, the current through the component also decreases to half of its initial value. This is per Ohm’s law, i.e., V °c I.

Question 30. On what factors does the resistance of a conductor depend?
Answer: The resistance of the conductor depends

1. On its length,
2. On its area of cross-section and the nature of its material.

Question 31. Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?
Answer: The current will flow more easily through a thick wire than a thin wire of the same material. The larger the area of the cross-section of a conductor, the greater the ease with which the electrons can move through the conductor. Hence the lower the resistance of the conductor.

Question 32. Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
Answer: The coils of electric toasters and electric irons are made of alloys instead of pure metal due to the following reasons:

Alloys have higher resistivity than that of their constituent metals.

Alloys do not oxidize (or burn) readily at high temperatures.

Question 33. Use the data to answer the following:

1. Which among iron and mercury is a better conductor?
2. Which material is the best conductor?

Answer: Resistivity of iron = 10.0 x 10-8 ft m Resistivity of mercury = 94.0 x 10-8 ft m Thus, iron is a better conductor because it has lower resistivity than mercury.

As silver has the lowest resistivity (= 1.60 x 10-8 ft m), silvers are the best conductor.

Question 34. Draw a schematic diagram of a circuit consisting of a battery of three cells of Veach, a 5 ft resistor, an S ft resistor a 12 ft resistor, and a plug key, all connected in series.
Answer: The Required circuit diagram is shown

Question 35. What determines the rate at which energy is delivered by a current
Answer: The resistance of the circuit determines the rate at which energy is delivered by a current.

Question 36. How is a voltmeter connected in the circuit to measure the potential difference between two points?
Answer: A voltmeter is connected in parallel to measure the potential difference between two points in a circuit

Chapter 12 Electricity Multiple Choice Questions

Question 1. A piece of wire of resistance is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance ofthis combination is’, then the ratio’ is:

1. 1/25
2. 1/5
3. 5
4. 25

Answer: Resistance of each part= r/5

When the five parts are connected in parallel, the equivalent resistance R’ is given by

⇒ \(\begin{aligned}
& \frac{1}{\mathrm{R}^{\prime}}=\frac{5}{\mathrm{R}}+\frac{5}{\mathrm{R}}+\frac{5}{\mathrm{R}}+\frac{5}{\mathrm{R}}+\frac{5}{\mathrm{R}}=\frac{25}{\mathrm{R}} \\
& \frac{\mathrm{R}}{\mathrm{R}^{\prime}}=25
\end{aligned}\)

Question 2. Which of the following terms does not represent electrical power in a circuit?

1. IR2
2. \P/R
3. PR
4. VI

Answer: IR2 does not represent electrical power.

Question 3. An electric bulb is rated 220 V and 100 W. When it is operated at 110 V, the power consumed will be:

1. 75 W
2. 25 W
3. 100 W
4. 50 W

Answer: 4. Resistance \(\mathrm{R}=\frac{\mathrm{V}^2}{\mathrm{P}}\)

⇒ \(\begin{aligned}
& =\frac{(220)^2}{100} \\
& =484 \Omega
\end{aligned}\)

When operated at 110 V, the power consumed will be

⇒ \(\begin{aligned}
P^{\prime} & =\frac{V^2}{R} \\
& =\frac{(110)^2}{484} \\
& =25 \mathrm{~W}
\end{aligned}\)

Question 4. Two conducting wires ofthe same material and of equal lengths and equal diameters are first connected in series and then in parallel in a circuit across the same potential difference. The ratio of produced in series and parallel combinations would be

1. 1:2
2. 2:1
3. 1:4
4. 4:1

Answer: Let R be the resistance of each wire. In series combination, the total resistance will be 2R. Heat produced.

Question 2. Why do V birds sitting on live wire get an electric shock?
Answer: Birds when sitting on the live wire just add to the circuit, it does not get shocked because the current is not flowing out of their body to any other material.

Question 3. There is a frill of 20 bulbs connected in series in a room. One bulb gets fused. The remaining 19 are again joined in series and connected to the same supply. Will the light increase or decrease in the room?
Answer: The light will increase.If the voltage remains the same, then the power available to the frill
\(\mathrm{P}=\frac{\mathrm{V}^2}{\mathrm{R}}\) where R is resistance ofthe frill. When one bulb is removed, the resistance of the frill decreases and hence the power output will increase.

Question 4. Two perform the experiments on series and andparallel combinations of two given resistors R1 and R2 and plot the following V-Igraphs

Which of the graphs is (are) correctly labeled in terms ofthe words ‘series and ‘parallel’1? Justify your answer.
Answer: In a series combination for a given voltage, the current is less as compared to that in a parallel combination. Therefore, both graphs are labeled correctly.

CBSE Class 10 Science Chapter 5 Periodic Classification Of Elements

Periodic classification of elements

CBSE Class 10 Science Chapter 5 Periodic Classification Of Elements Definitions

1. Need for classification:

One hundred and fourteen elements are forming millions of compounds. Though initially fewer elements were known (63 at the time of Mendeleev) there was a need to arrange the elements in a certain order to summarise their properties.

2. Dobereiner (1817) grouped the elements with similar properties in triads so that the atomic mass of the middle element was average of the other two

Example: triads: N, P, As, Ca, Sr. Ba and Cl. Br, I.

Read and Learn More CBSE Class 10 Science Short Answer Questions

3. Newlands (1866) gave the law of octaves. He found that every eighth element had properties similar to that of the first when arranged in increasing order of their atomic masses.

4 . Lother Meyer made a plot of atomic volumes of elements against their atomic masses. He found that similar elements occupied similar positions on the curve.

5. Mendeleev’s Periodic Table: He arranged the elements in increasing order of their atomic masses.

6. Modern Periodic Law: The physical and chemical properties of elements are the periodic function of their atomic number.

7. The Modern Periodic Table is based on modern periodic law which states that “properties of elements are a periodic function of their atomic numbers.” The periodicity in the properties of elements could be related to the periodicity in their electronic configurations. Modem Periodic Table is divided into 18 vertical columns called groups and 7 horizontal rows called periods.

8. Trends in the Modern Periodic Table

1. In a group, the number of valence electrons remain the same. One in group, or three in group 3. On moving from left to right in a period, the number of valence electrons increases from one to eight.
2. Atomic size increases down a group because of the addition of new shells. While in a period, the atomic size decreases from left to right. (Extra nuclear charge but no extra shell).
3. Metallic and non-metallic character: Metallic character increases down a group (ease of loss of electron increases) and decreases along a period. Non-metallic character increases along a period from left to right.
4. Ionization energy increases across a period (energy required to remove the most loosely bound electron from a gaseous neutral atom). This also follows that ionization energy decreases down a group.

9. Chemical reactivity:

On moving from left to right in a period, the chemical reactivity first decreases (Na→Mg→ Al→ Si) and then increases (P→ S→Cl  example for 3rd period.

10. Ionisation energy:

Ionisation energy is the energy required to remove an element. It is expressed in kJmol^-1

Ag(g) +I.E → Ag⁺(g) +e^–

When more than one electron is to be removed, more energy is required because in this case electron is to be removed from the unipositive ion. Similarly, subsequent ionization energy will be still greater. i.e.,

1 st ionisationenergy <2 nd ionosationenergy <3 rd ionisation energy.

11. Electron affinity:

Whenever an atom gains an electron, energy is released. Thus electron affinity is the energy released when an electron is gained by a neutral gaseous atom to become a negatively charged ion.

For example:

12. Important characteristics of a period in the periodic table:

Valence electrons:

On moving from left to right in a period, the number of valence electrons increases from one to eight (except in the first period where the increase is from one to two only.)

 Valency:

The valency of elements increases from one to four, then decreases to one and becomes zero in the case of inert gases.

For example:

In compounds LiCl, BeCl₂, BCl₃ and CCl₄ the valency of Li, Be, B and C are 1, 2, 3 and 4 respectively. Whereas in compounds, NH₃, H₂O, and HF, the valency of N, O, F are 3, 2 and 1 respectively.

Zero group: At the end of each period is the zero group element, the inert gas.

Size of atoms:

Atomic radii of the elements decrease gradually from left to right in a period because the nuclear charge increases but no extra shell is added.

Metallic character:

Metallic character decreases from left to right across a period and non-metallic character increases.

Ionisation energy:

Ionisation energy increases across a period from left to right. Ionisation energy is the energy required to remove the most loosely bound electron from a neutral gaseous atom.

Chemical reactivity:

On moving from left to right in a period, the chemical activity of elements first decreases and then increases. For example, in the third period, Na is very reactive, Mg, and Al are less reactive, Si is least reactive and the reactivity increases from P, S to Cl.

Oxides: The basic character of the oxides of the elements decreases and the acidic nature of the oxides of the elements increases.

For example:

In the 3rd period starting with sodium oxide, it is highly basic, and the next magnesium oxide is less basic. Then comes aluminium and silicon which give amphoteric oxides. They are the oxides of phosphorus and sulphur which are acidic. And the last chlorine oxide is highly acidic.

Electronegativity: Electronegativity increases on moving across a period from left to right. It is a measure of the tendency of the element to attract electrons towards itself.

13. Characteristics of a group:

Valency: In a group all the elements have the same valency.

For example:

group elements: Li, Na, K etc., all have a valency of +1. Elements ofgroup 17: Cl, Br, I etc. all have a valency of-1.

Size of atoms:

Atomic radii or the size of atoms of the elements increase on going down a group. This is due to the addition of new electronic shells.

Metallic character:

On descending a group the metallic character increases. For example, groups 14 and 15 begin with carbon and nitrogen which are non-metals. These groups end with lead and bismuth respectively which are metals. The oxides of the elements become increasingly basic.

Melting and boiling points:

The melting and boiling points of metals decrease on going down in a group.

Ionisation energy:

Ionisation energy decreases on moving down a group with the increase in atomic number. This is because the size of the atom increases and the valence electrons are farther removed from the attractive effect of the nucleus.

Chemical reactivity:

The chemical reactivity of metals increases on going down a group. For example, in group 1 of alkali metals, the chemical reactivity increases from lithium to francium. On the other hand, the chemical reactivity of metals decreases on going down in a group.

For example:

In group 17 of halogen elements (non-metals), fluorine is the most reactive and iodine is the least reactive

CBSE Class 10 Science Chapter 5 Periodic Classification Of Elements Short Question And Answers

Question 1. Did Dobereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.
Answer:

Yes, Dobereiner’s triads also existed in the columns of Newlands’ Octaves. For example, if you examine the first column ofNewlands’ Octave which has elements like

Lithium (Li), Sodium (Na) and Potassium (K). This also constituted Dobie Reiner’s triad: Li

⇒ \(\mathrm{Na}(23), \mathrm{K}(39)\left[\frac{7+39}{2}=23\right]\)

Question 2. What were the limitations ofDobereiner’s classification?
Answer:

Dobereiner’s classification could give only a limited no. of triads. Further, there were other elements which resembled a lot of triads but could not be accommodated. He could identify only three triads from the elements known at that time.

Question 3. What were the limitations of the Newlands of Octaves?
Answer:

Limitations of Newlands’ Law of Octaves:

The law of Octaves was applicable only upto Calcium (At. wt. = 40). After this every eighth element did not possess properties similar to that of the first as against his postulate. Though 56 elements were known at that time.

To fit elements into his table, at places he adjusted two elements into one slot. Cobalt (Co) and Nickel (Ni) were put in one slot and these were placed in the same column as Fluorine (F), Chlorine (Cl) and Bromine (Br) which have entirely different properties.

Iron (Fe) which resembles Cobalt and Nickel in properties, was placed far away

Question 4. Besides gallium, other elements have since been discovered that were left by Mendeleev in his periodic table. (Any two)
Answer:

Besides Gallium (Ga): The following two elements were discovered for the gaps left by

Mendeleev in his periodic table.

Scandium (Sc) and Germanium (Ge).

Question 5. Why are the noble gases placed in a separate group?
Answer:

Noble gases like Helium (He), Neon (Ne), and Argon (Ar) are chemically inert and are present in atmosphere in minimal concentrations. Thus, owing to their inert chemical behaviour and similar electronic configuration, they are justified to be placed in a separate group

Question 6. How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table?
Answer:

By considering that the properties of elements are periodic functions of their atomic numbers, the following anomalies of Mendeleev’s periodic table were removed.

The anomaly of keeping isotopes in the same slot was solved as isotopes have similar properties and have the same atomic number but different atomic masses.

The atomic masses of the elements do not increase regularly in going from one element to the next but atomic numbers do. Now placement of hydrogen with alkali metals is justified based on their electronic configuration.

Question 7. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?
Answer:

Beryllium (Be) and Calcium (Ca) will show similar chemical properties to that of Magnesium (Mg).

Basis of choice:

The basis of these two elements Be (at. no. 4) and Ca (at. no. 20) is that these belong to the same group and have the same number of outermost electrons of magnesium

Mg – 2,8,2

Be -2,2

Ca- 2,8,8,2

All three react with oxygen to give basic oxides such as MgO, BeO and CaO.

Question 8.

1. Name Three elements that have a single electron in their outermost shells.
2. Two elements that have two electrons in their outermost shells.
3. Three elements with filled outermost shells.

Answer:

1. Lithium (2, 1), Sodium (2, 8, 1) and Potassium (2, 8, 8, 1).
2. Magnesium (2, 8, 2), Calcium (2, 8, 8, 2).
3. Helium (2), Neon (2, 8), Argon (2, 8, 8).

Question 9. Which ofthe following statements is not a correct statement about the trends when going from left to right across the periods ofPeriodic Table?

1. The elements become less metallic.
2. The number of valence electrons increases.
3. The atoms lose their electrons more easily.
4. The oxides become more acidic.

Answer:

The atoms lose their electrons easily when going from left to right is not correct.

Question 10. Element X forms a chloride with the formula XCl2, which is a solid with a high melting point. X would most likely be in the same group ofthe Periodic Table as

1. Na
2. Mg
3. AI
4. Si

Answer: 2. Mg. (X is bivalent)

Question 11. Which element has

1. Two shells, both of which are filled with electrons?
2. The electronic conjuration 2, 8, 2?
3. A total of three shells, with four electrons in its valence shell?
4. A total of two shells, with three electrons in its valence shell?
5. Twice as many electrons in its second shell as in its first shell?

Answer:

Neon, Ne (2, 8)

Silicon, Si (2, 8, 4)

Question 12.

1. What properties do all elements in the same column ofthe Periodic Table as boron have in common?
2. What properties do all elements in the same column of the Periodic Table as fluorine have in common?

Answer:

1. The elements in the same column as Boron have three electrons in their outermost shell just like Boron. All are metalloids.
2. Elements in the same column as Fluorine have seven electrons in their outermost shell and form acidic oxides like Fluorine does.

Question 13. Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?
Answer:

Electronic configuration of (7): 2, 5.

Electronic configuration of (15): 2, 8, 5.

Nitrogen will be more electronegative than phosphorous because the outermost shell in nitrogen is nearer to the nucleus and thus positive nucleus will attract electrons strongly.

Question 14. How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?
Answer:

The position ofan atom/element in the periodic table is related to the number ofelectrons in the outermost shell. In a given column or group, all elements have the same number of electrons in their outermost shells.

For example: In group II, all elements have two electrons in their outermost shell. In group 15, all elements have 5 electrons in their outermost shells.

Question 15. Choose from the following: ₂₀Ca, ₃Li, ₁₁Na, ₁₀Ne

1. An element having 2 shells completely filled with electrons.
2. Two elements belonging to the same group ofperiodic table.

Answer:

₁₀Ne has electronic configuration 2, 8. Both shells are completely filled.

₃Li and ₁₁Na belong to the same group i.e. 1st group.

Question 16. Write two achievements of Mendeleev’s periodic table.
Answer:

1. It could classify all the elements discovered at that time.
2. It helped in the discovery of new elements.

Question 17.

1. Name the element with atomic number 17.
2. To which period does it belong?
3. To which group does it belong?
4. Write its electronic configuration.

Answer:

1. Chlorine
2. 3rd
3. 17th
4. K – 2 , L -8 , M – 7

Question 18. An element X(atomic number 17) reacts with an element Y(atomic number 20) to form a divalent halide.

1. What is the position of elements X and Yin in the periodic table?
2. What will be the nature of the oxide of element Y? Identify the nature of bonding in the compound formed.

Answer:

X- non-metal

Y- metal

YX₂

1. X- Position- Group- 17, period- 3

Y- Position- Group- 2, Period- 4

2. Basic YO, ionic bond.

Question 19. Two elements M and N belong to group 1 and 2 respectively and are in the same period of the periodic table. How do the following properties of M and N vary:

1. Sizes oftheir atoms
2. Their metallic characters
3. Their valencies in forming oxides
4. Formulae oftheir chlorides

Answer: The size of atom decreases from left to right. Atom ofM is bigger than atom ofN.

M is more metallic than N.

Group 1: Valency 1

Group 2: Valency 2

Formulae of chloride: MCI, NCl₂

Question 20. On the basis of electronic configuration, how will you identify the first and the last element of a period.
Answer:

Ist element has 1 valence electron and last element has 8 valence electrons. A number of shells remain the same in the same period.

Question 21. Explain the basic character of oxide ofelements down the group and across the period.
Answer:

The basic nature decreases across the period.It changes from basic to acidic.

The basic nature increases down the group.

These variations in the acidic and basic nature of oxides canbe related to the electronegativity of the element.

As the electronegativity of the element increases along a period the acidic character of the oxide increases and as the electronegativity of the element decreases down the group the basic character of the oxide increases.

Question 22. Describe the basic character ofthe oxides of third period elements across the period from left to right.
Answer:

The basic nature decreases across the period.

Na and Mg are basic.

Al and Si are amphoteric.

P, Cl, and S are acidic.

Question 23. List the anomalies of Mendeleev’speriodic table which were renamed by modern periodic law.
Answer:

Anomalies of Mendeleev’s periodic table:

1. The correct position of hydrogen was not assigned.
2. The position of isotopes was not defined.
3. Placement of heavier element before lighter element.

Question 24.

1. Amongst the following elements identify the ones that would form anions: K, O, Na, F, Ca.Cl, Mg
2. Write the electronic configuration of anions identified above.

Answer:

O, F and Cl would form anions.

O^2- = 2, 8

F^– = 2, 8

Cl^–= 2, 8,8

Question 25. “Elements in Periodic Table showperiodicity of properties.”List any four such properties.
Answer:

1. Atomic size
2. Valency or combining capacity
3. Metallic property
4. Non-metallic property

Question 26. Mention any two trends exhibited by elements when we go from left to right across the period of the periodic table.
Answer:

1. Atomic radius decreases.
2. Metallic character decrease.

Question 27. State the reason for the following:

1. The elements of the same group have similar chemical properties.
2. The elements ofthe same period have different properties.

Answer:

1. Because of a same number of valence electrons.
2. Because of different numbers of valence electrons

Question 28. Calcium is an element with the atomic number 20.

1. Is it a metal or a non-metal?
2. Is it more reactive than Mg or less?
3. What will be its valency?
4. What will be the formula of its chloride?

Answer:

1. It is a metal.
2. It is more reactive than Mg.
3. Its valency is 2.
4. CaCl₂.

Question 29. What are metalloids? How many electrons can he present in the valence shell of their atoms? In which part of the periodic table these are located? What type of oxides are formed by these elements?
Answer:

Metalloids are elements which resemble both metals and non-metals. The valence shell of metalloids contains 3, 4, 5, and 6 elements starting from periods 2 to 5 respectively. These are found on the right side of the table in the zig-zag column,

Example: Boron, silicon, germanium, arsenic etc. These form amphoteric oxides.

Question 30. What is electronegativity? How does it compare with electron affinity?
Answer:

Though both Electronegativity and Electron Affinity refer to the attraction of electrons but are used in different contexts. Electronegativity refers to the attraction of bonding electrons or shared pairs of electrons whereas Electron Affinity refers to the attraction of electrons by an isolated gaseous atom.

Question 31. Given below are some elements ofthe modern periodic table. The atomic number of the elements are given in parentheses: A (4), B (9), C (14), D (19), E (20)

1. Select the element that has one electron in the outermost shell. Also, write the electronic configuration of this element.
2. Which two elements amongst these belong to the same group? Give a reason for your answer.
3. Which two elements amongst these belong to the same period? Which one of the two has a bigger atomic radius?

Answer:

1. D ; 2, 8, 8, 1

2. A and E belong to the same group as both have the same number of valence electrons i.e., same number of electrons (2) in the outermost shell.

3. A and B/D and E. A has a bigger atomic radius than B or D has a bigger atomic radius than E.

Question 32. The three elements A, B, and C with similar properties have atomic masses X, Y, and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called as? Give one example of such a set of elements.
Answer:

Dobereiner triad;

Example:  Lithium, Sodium, Potassium

Question 33. Elements have been arranged in the following sequence based on their increasing atomic masses. F, Na, Mg, Al, Si, P, S, Cl, Ar, K

1. Pick two sets of elements which have similar properties.
2. The given sequence represents which law of classification of elements?

Answer:

1.

1. F and Cl
2. Na and K

2. Newlands’ law of octaves.

Question 34. Can the following groups of elements be classified as Dobereiner’s triad?

1. Na, Si. Cl
2. Be. Mg, Ca

Atomic mass of Be 9; Na 23; Mg 24; Si 28; Cl 35; Ca 40

Explain by giving a reason.

Answer:

No, because all these elements do not have similar properties although the atomic mass of silicon is average of atomic masses of sodium (Na) and chlorine (Cl).

Yes, because they have similar properties and the mass of magnesium (Mg) is roughly the average of the atomic mass ofBe and Ca.

Question 35. In Mendeleev’s Periodic Table, the elements were arranged in the increasing order of their atomic masses. However, cobalt with atomic mass of  58.93 amu was placed before nickel having an atomic mass of 58.71 amu. Give a reason for the same.
Answer:

1. The properties of cobalt are similar to those of Rhodium and Iridium (Ir) (the same group) and.
2. The properties of nickel are similar to those of Palladium (Pd) and Platinum (Pt) (same group).

Question 36. “Hydrogen occupies a unique position in Modern Periodic Table”. Justify the statement.
Answer:

Though hydrogen is a non-metal, it has been placed at the top of group-1 above the alkali metals because its electronic configuration is similar to alkali metals i.e., (have valence electronin the outermost shell). But while discussing the alkali metals, hydrogen is not considered. Thus, hydrogen occupies a unique position is modern periodic table.

Question 36. Three elements A, B, and C have 3, 4 and 2 electrons respectively in their outermost shell. Give the group number to which they belong in the Modern  Periodic Table. Also, give their valencies
Answer:

Question 38. Compare the radii of two species X and Y. Give reasons for your answer.

1. X has 12 protons and 12 electrons
2. Y has 12 protons and 10 electrons

Answer:

1. Radii of Y < Radii of X
2. Because Y is the cation of X.

Question 39. Arrange the following elements in increasing order oftheir atomic radii’

1. Li, Be, F, N
2. Cl, At, Br,I

Answer:

1. F < N < Be < Li
2. Cl < Br <I < Al

Question 40. Identify and name the metals out ofthe following elements whose electronic configurations are given below:

1. 2, 8, 2
2. 2, 8, 1
3. 2, 8, 7
4. 2, 1

Answer:

(1), (2) and (4)

1- Magnesium

2 – Sodium

4 – Lithium

Question 41. Write the formula of the product formed when the element A (atomic number 19) combines with the element B (atomic number 17).

Draw its electronic dot structure. What is the nature ofthe bond formed?

A = K (Potassium)

B = Cl (Chlorine)

Question 42. Arrange the following elements in the increasing order oftheir metallic characters Mg, Ca, K, Ge, Ga
Answer:

Ge < Ga < Mg < Ca < K

Question 43. Identify the elements with the following properties and arrange them in increasing order of their reactivity

1. An element which is a soft and reactive metal
2. The metal which is an important constituent of limestone
3. The metal which exists in a liquid state at room temperature

Answer:

1. Na or K
2. Hg
3. Increasing order oftheir reactivity as Hg < Ca < Mg < Ca < K

Question 44. What are metalloids? How many electrons can be present in the valence shell of their atoms? In what part of the periodic table these are located? What type of oxides are formed by these elements?
Answer:

Metalloids are elements which resemble both metals and non-metals. The valence shell of metalloids contains 3, 4, 5, 6 elements starting from periods 2 to 5 respectively. These are found on the right side of the table in the zig-zag column,

Examples: Boron, silicon, germanium, arsenic, etc. These form amphoteric oxides.

CBSE Class 10 Science Chapter 5 Periodic Classification Of Elements Multiple Choice Questions

Question 1. Upto which element, the Law ofOctaves was found to be applicable

1. Oxygen
2. Calcium
3. Cobalt
4. Potassium

Answer: 2. Calcium

Question 2. According to Mendeleev’s Periodic Law, the elements were arranged in the periodic table in the order of

1. Increasing atomic number
2. Decreasing atomic number
3. Increasing atomic masses
4. Decreasing atomic masses

Answer: 3. Increasing atomic masses

Question 3. In Mendeleev’s Periodic Table, gaps were left for the elements to be discovered later. Which ofthe following elements found a place in the periodic table later?

1. Chlorine
2. Silicon
3. Germanium
4. Oxygen

Answer: 1. Chlorine

Question 4. Which of the following statement (s) about the Modern Periodic Table are incorrect?

1. The elements in the Modern Periodic Table are arranged on the basis oftheir decreasing atomic number

2. The elements in the Modern Periodic Table are arranged on the basis oftheir increasing atomic masses

3. Isotopes are placed in adjoining group(s) in the Periodic Table

4. The elements in the Modern Periodic Table are arranged based on their increasing atomic number

1. 1 Only
2. 1, 2 and 3
3. 1, 2 and 4
4. 4 only

Answer: 2. 1, 2 and 3

Question 5. Which ofthe following statements about the Modern Periodic Table is correct?

1. It has 18 horizontal rows known as Periods
2. It has 7 vertical columns known as Periods
3. It has 18 vertical columns known as Groups
4. It has 7 horizontal rows known as Groups

Answer: 3. It has 18 vertical columns known as Groups

Question 6. Which ofthe given elements A, B, C, D, and E with atomic numbers 2, 3, 7, 10 and 30 respectively belong to the same period?

1. A, B, C
2. B, C, D
3. A,D,E
4. B, D, E

Answer: 2. B, C, D

Question 7. The elements A, B, C, D, and E have atomic number 9, 11, 17, 12 and 13 respectively. Which pair of elements belong to the same group?

1. A and B
2. A and C
3. B and D
4. D and E

Answer: 3. B and D

Question 8. Where would you locate the element with electronic configuration 2, 8 in the Modern Periodic Table?

1. Group 8
2. Group 2
3. Group 18
4. Group 10

Answer: 3. Group 18

Question 9. An element which is an essential constituent of all organic compounds belongs to

1. Group 1
2. Group 14
3. Group 15
4. Group 16

Answer: 2. Group 14

Question 10. Which ofthe following is the outermost shell for elements of period 2?

1. K shell
2. M shell
3. L shell
4. N shell

Answer: 2. M shell

Question 11. Which one ofthe following elements exhibits a maximum number of valence electrons?

1. Na
2. Al
3. Si
4. P

Answer: 4. P

Question 12. Which ofthe following gives the correct increasing order ofthe atomic radii of

1. O, F,N
2. N, F, O
3. O, N, F
4. F,O, N

Answer: 4. F, O,N

Question 13. Which among the following elements has the largest atomic radii?

1. Na
2. Mg
3. COK
4. Ca

Answer: 3. COK

Question 14. Which ofthe following elements would lose an electron easily?

1. Mg
2. Na
3. K
4. Ca

Answer: 3. K

Question 15. Which ofthe following elements does not lose an electron easily?

1. Na
2. F
3. Mg
4. Al

Answer: 2. F

Question 16. Which ofthe following are the characteristics of isotopes ofan element?

1. Isotopes ofan elements have same atomic masses

2. Isotopes ofan elements have same atomic number

3. Isotopes ofan elements show same physical properties

4. Isotopes ofan elements show same chemicalproperties

1. 1, 3 and 4
2. 2,3 and 4
3. 2 and 3
4. 2 and 4

Answer: 4. 2 and 4

Question 17. Arrange the following elements in the order oftheir decreasing metallic characters Na, Si, Cl, Mg, Al

1. Cl > Si >Al > Mg >Na
2. Na >Mg > Al > Si > Cl
3. Al >Na >Si>Ca> Mg
4. Na >Al> Mg > Cl >Si

Answer: 2. Na >Mg > Al > Si > Cl

Question 18. Arrange the following elements in the order oftheir increasing non-metallic characters Li, O, C, Be, F

1. F < O < C < Be <Li
2. Li < Be < C < O <F
3. F < O < C < Be <Li
4. F < O < Be < C <Li

Answer: 2. Li < Be < C < O <F

Question 19. What type of oxide would Eka-aluminium form?

1. EO₃
2. E₃O₂
3. E₂O₃
4. EO

Answer: 3. E₂O₃

Question 20. Three elements B, Si and Ge are

1. Metals
2. Non-metals
3. Metalloids
4. Metal, non-metal and metalloid respectively

Answer: 3. Metalloids

Question 21. Which ofthe following elements will form an acidic oxide?

1. An element with atomic number 7
2. An element with atomic number 3
3. An element with atomic number 12
4. An element with atomic number 19

Answer: 1. An element with atomic number 7

Question 22. The element with atomic number 14 is hard and forms acidic oxide and a covalent halide.

1. To which ofthe following categories does the element belong?
2. Metal
3. Metalloid
4. Left-hand side elements

Answer: 3. Metalloid

Question 23. Which one of the following depicts the correct representation of the atomic radius of an atom?

1. 1 and 2
2. 2 and 3
3. 3 and 4
4. 1and 4

Answer: 2. 2 and 3

Question 24. Which one ofthe following does not increase while moving down the group of the periodic table?

1. Atomic radius
2. Valency
3. Metallic character
4. Number of shells in an element

Answer: 3. Metallic character

Question 25. On moving from left to right in a period in the periodic table, the size ofthe atom

1. Increases
2. Decreases
3. Does not change appreciably
4. First decreases and then increases

Answer: 2. Decreases

Question 26. Which of the following sets of elements is written in order of their increasing metallic character?

1. Be, Mg, Ca
2. Na, Li, K
3. Mg,Al,S
4. C, O, N

Answer: 1.Be, Mg, Ca

CBSE Class 10 Science Chapter 16 Management Of Natural Resources

Management of natural resources:

CBSE Class 10 Science Chapter 16 Management Of Natural Resources Definitions

1. Natural resources will last for generations to come and will not merely be exploited to the hilt of short-term gains.
2. The Ganga Action Plan was taken by the Government to save the river Ganga (1985).
3. Coliform bacteria is a group of bacteria, the presence of which confirms the
   contamination of water of a river.
4. The R’s to save the environment
   • Reduce
   • Recycle
   • Reuse.
5. Renewable resources are those which can replenish themselves within a reasonable time.
6. Non-renewable resources are those which lack the ability of replenish and replacement
7. Development that lasts is called sustainable development.
8. Silviculture is one of the major programs started to replenish forests.
9. Conservation of wildlife in natural habitats is called in situ conservation.
10. Conservation of wildlife away from their natural habitats is called exsitu conservation.
11. Biosphere reserves deal with the conservation of ecosystems and the genetic resources contained therein.
12. A dam is a barrier built across a stream or river to hold and control the flow ofwater for useful purposes.
13. WCD stands for World Commission of Dams.
14. Water harvesting is the activity of direct collection of rainwater, which can be stored for direct use or can be recharged into the groundwater.
15. Various compounds of the harvesting system are Collection of rainwater, filtration, storage, recharge, and use.
16. The Tawa Irrigation Project in Madhya Pradesh has resulted in problems of waterlogging and increased salinity.
17. Project Tiger was started in 1973 to check the reduction of the population of tigers.
18. Three fossil fuels are coal, petroleum, and natural gas.
19. Sustainability is defined as meeting the needs of the present generation without
    compromising the ability of future generations to meet their own needs.
20. Coal is a mixture of free carbon and compounds of carbon containing carbon, hydrogen, oxygen, nitrogen, and sulfur.
21. Petroleum is also called rock oil.
22. Petroleum is a mixture of hydrocarbons mainly alkanes, cycloalkanes, and aromatic hydrocarbons.
23. Environment ethics means a set ofmoral principles connected with our responsibility to keep our environment clean.
24. The Chipko movement is one of the movements in India to conserve biodiversity.
25. IUCN (International Union for Conservation of Nature and Natural Resources) was set up in 1948 for the practical implementation of environmental laws. It was sponsored by UNESCO.
26. The year 1972 was declared as International Year of Conservation of Nature

Read and Learn More CBSE Class 10 Science Short Answer Questions

CBSE Class 10 Science Chapter 16 Management Of Natural Resources Short Question And Answers

Question 1. What changes can you make in your habits to become more environment-friendly?
Answer:

1. By not using polythene bags.
2. By not using products like fur, and ivory derived from wildlife.
3. By planting one tree every year and watching it grow.
4. By using a bucket of water instead of bathing under the shower.

Question 2. Why do you think there should be an equitable distribution of resources? What forces would be working against an equitable distribution of our resources?
Answer:

There should be an equitable distribution of resources to fulfill the needs of every citizen without any discrimination between rich and poor. Presently power and money are the two forces that are working against the equitable distribution of resources.

Question 3. Why should we conserve forests and wildlife?
Answer:

We should conserve forests as they are hot spots of biodiversity.Ifwe do not conserveit willlead to ecological imbalancein nature. Forests maintain biological diversity, preventing soil and flood erosion apart from influencing rainfall.

Question 4. Suggest some approaches towards the conservation of forests.
Answer:

1. By checking unnecessary deforestation.
2. By preventing forest fires.
3. Reforestation.
4. By not allowing overgrazing in forests.

Question 5. Compare the above system with the probable systems in hilly mountainous areas, plains, or plateau regions.
Answer:

In a large level terrain, the water harvesting structures are mainly current-shaped earthen embarkments, or low straight concrete and rubble ‘check dams’ built across seasonally flooded gullies. Monsoon rains fill the ponds behind the structures.

Question 6. Find out the source of water in your region’s locality. Is water from this source available to all people living in that area?
Answer:

In our locality water is mostly supplied by government agencies through taps. This water is mainly drawn from the river or tubewells. However, this water is available only in those areas which are approved by local civic authorities.

Note: (The answer to the question will differ for rural and urban areas). For rural areas the answer will be: In our areas, we get water from wells, ponds, hand pumps, or rivers.

Question 7. What changes would you suggest in your home to be environment-friendly?
Answer:

We should use the principle of three R’s to be environment-friendly which are:

• Reduce the use of national resources to a reasonable amount.
• Recycle plastic, paper, glass, and other items that can be recycled.
• Reuse the things again e.g., used envelopes, bottles, and cans.

Question 8. Can you suggest some changes in your school which would make it environment-friendly?
Answer:

1. Planting trees around the school campus.
2. Separation of biodegradable and non-biodegradable wastes.
3. Minimize the use of fans and other electrical appliances by switching them off when not required.
4. Avoiding waste of drinking water.

Question 9. We saw in this chapter that there are four main stakeholders when it comes to forests and wildlife. Which among these should have the authority to decide the management of the produce? Why do you think so?
Answer:

Local people living around the forests should be the authority to decide the management of various forest products. The reason is that these people are aware ofthe various practices to use the resources sustainably. These people have been using the forest and wildlife resources for centuries without harming or causing any damage to the environment.

Question 10. How can you as an individual contribute or make a difference to the management of

1. Forests and wildlife
2. Water resources, and
3. Coal and petroleum?

Answer:

1. I will not allow cutting of trees and overgrazing in a forest.
2. I will use water in such a way that there is no waste at all.
3. I will not burn coal to heat my room in winter instead I wear an extra sweater. Walk to school instead of insisting my parents drop me at school on their bike/car

Question 11. What can you as an individual do to reduce your consumption of the various natural resources?
Answer:

1. Reducing the usage of products obtained from wildlife.
2. Avoiding wastage of water.
3. Minimizing the use of coal and petrol.

Question 12. We often observe domestic waste decomposing in the bylanes of residential colonics. Suggest ways to make people realize that the improper disposal of waste is harmful to the environment.

Answer:

1. It can act as a reservoir for the breeding of disease-causing pathogens.
2. It can release greenhouse gases which can result in global warming.

Question 13. What are the disadvantages of using fossil fuels?
Answer:

1. Burning of fossil fuel causes air pollution due to the release of oxides of sulfur and nitrogen.
2. Fossil fuel is non-renewable; if used at the current rate it will last for a few years.

Question 14. List any two advantages associated with water stored in the ground.
Answer:

Advantages:

1. Recharges the groundwater.
2. Prevents evaporation of water.
3. Prevents breeding of mosquitoes.
4. Prevents contamination.

Question 15. What is reuse strategy? Reuse strategy is considered better than the recycling strategy?
Answer:

In the reuse strategy, things are used again and again instead of throwing them.

It is better than recycling objects as no energy is used in this strategy for remaking objects.

Question 16. In which way groundwater is more advantageous as compared to surface water?
Answer:

1. In ground water mosquitoes cannot breed.
2. It does not evaporate.
3. It remains protected from contamination by human and animal waste.

Question 17. In which way does the management of fossil fuels like coal and petroleum differ from other natural resources?
Answer:

Coal and petroleum were formed from the degradation of biomass millions of years ago and their source is limited. These resources will be exhausted in the future no matter how carefully we use them. Because of these reasons such resources involve slightly different approaches.

Question 18.

1. Why are CIKII and petroleum called fossil fuels?
2. Name any two elements present in fossil fuels in addition to carbon.

Answer:

1. They are formed from the preserved remains of organisms that lived millions of
   years ago and are used as fuels.
2. Hydrogen, Sulfur.

Question 19. What is meant by biodiversity? List two advantages of conserving forests and wildlife.
Answer:

Biodiversity is the range and number of species of living organisms in a given area.

Two advantages:

1. Maintains ecological balance
2. Helps in maintaining rainfall.

Question 20. Why is it said that the “use of fossil fuels should be done judiciously?”
Answer:

The fossil fuels, coal, and petroleum, will ultimately be exhausted. Because of this and because their combustion pollutes our environment, we need to use these resources judiciously.

Question 21. Who are the stakeholders in respect of forests? Which one of these causes maximum damage to forests and how?
Answer:

Stakeholders in respect of forests are those people who utilize various forest products.

These are:

• The people who live in and around the forests.
• Industrialists engaged in manufacturing furniture, bidis, plywood, and sports goods.
• Forest department of government.
• Wildlife and nature enthusiasts, the industrialists cause maximum damage to forests as they consider the forest as merely a source of raw material for their factories.

Question 22. Differentiate between biodegradable and non-biodegradable substances with the help of one example each. List two changes in habit that people must adopt to dispose of non-biodegradable waste, to save the environment.
Answer:

Biodegradable substances can be broken down into simpler substances by nature/decomposers/bacteria/saprophytes, e.g., human excreta, vegetable peels, etc.

Non-biodegradable wastes cannot be broken down into simpler substances by nature/decomposers,

Example: Plastic, glass.

Habits:

1. Use of separate dustbins for biodegradable and non-biodegradable waste.
2. Reuse of things such as polybags etc.
3. Recycle of wastes.

Question 23. Prepare a list of five items that you use daily in the school. Identify from the list such items that can be recycled.
Answer:

Paper, resin bag, blade, pen, plastic box, scale, eraser, compass and dividers (metallic), steel lunch box, steel spoon. Paper, blades, plastic boxes, erasers, compasses, steel lunch boxes, and steel spoons canbe recycled.

Question 24. List two advantages associated with water harvesting at the community level.
Answer:

Water harvesting is a method of holding rainwater on the surface ofthe earth, to make it percolate under the ground so as to recharge groundwater. Two advantages associated with water harvesting at the community level are:

Giving people control over their local water resources ensures that mismanagement is reduced.

Over-exploitation of these resources is reduced. The water stored in the ground does not evaporate, provides moisture for vegetation over a wide area, and is protected from contamination by human and animal waste.

Question 25. In a village in Karnataka, people started cultivating crops all around a lake which was always filled with water. They added fertilizers to their field to enhance the yield. Soon they discovered that the water body was completely covered with floating plants and fishes started dying in large numbers.

Analyze the situation andgive reasons for the excessive growth of plants and the death of fish in the lake.
Answer:

Since people used excessive fertilizers in the fields, they were carried down to the lake during rains. As many fertilizers contain phosphates and nitrates, the water body becomes enriched with these chemicals.

These chemicals promote excessive growth of aquatic plants and the surface of water is completely covered with plants (eutrophication). Depletion of light in the water body and insufficient availability of dissolved oxygen and nutrients resulted in the death of fish.

Question 26. What measures would you take to conserve electricity in your house?
Answer: The following measures can be taken to conserve electricity in our house:

Put off the fans and lights in unoccupied rooms and when they are not required. Maximize the use of solar radiation. It is a pollution-free and cost-free resource that is easily available.

During winter, instead of electric heaters, solar water heating systems should be usedFluorescentnt tubes or CFL should be used instead of electric bulbs as the former consume less electricity.

Question 27. Although coal and petroleum are produced by the degradation of biomass, yet we need to conserve them. Why?
Answer:

Both the energy sources coal and petroleum take millions of years for their formation. As these resources are being utilized at a much faster rate than their formation, they will be exhausted shortly, hence they need to be conserved.

Question 28. Suggest a few measures for controlling carbon dioxide levels in the atmosphere.
Answer:

A few measures for controlling carbon dioxide levels in the atmosphere are as follows:

1. Reduce the consumption of petrol in automobiles. Using carpools and public transport helps to reduce petrol usage.
2. Use of alternative fuels such as CNG (clean fuel) instead of coal and petroleum.
3. Manure should be prepared out of litter instead of burning it.
4. The smoke coming out ofthe thermal power stations and other industries should be well traded to remove harmful gases, before discharging them into the atmosphere.
5. Planting more and more trees.

Question 29. Why are the Arabari forests of Bengal known to be a good example of a conserved forest?
Answer:

The forest department developed a strategy in which the villagers were involved in the protection of the forest. In return for the labor, the villagers were paid and also had some benefitin harvesting operations.

They were allowed to collect wood and fodder on payment of a nominal fee. In this way, by the active and willing participation ofthe local people, the sal forests of Arabari were conserved.

Question 30. Is water conservation necessary? Give reasons.
Answer:

The total amount of fresh water is more than enough to meet the needs of human beings.

But its uneven distribution, wide seasonal as well as yearly fluctuation in rainfalls and water storage are chronic problems in most parts of the world.

Question 31. Prejudice against the traditional use of forest areas has no basis. Explain by giving an example.
Answer:

In many forests, the local population may not be allowed to use forests in the manner they have been using them for generations. This may sometimes be harmful to the sustainability of forests. When the nomadic shepherds were not allowed in the alpine meadows of the great Himalayan National Park to graze their sheep, it hurt the growth of grass.

Question 32. How did the ‘Chipko Andolan’ ultimately benefit the local population? Give any two benefits.
Answer:

• The Chipko movement quickly spread across communities and media, and forced the government, to whom the forest belongs, to rethink their priorities in the use of forest produce.
• Due to the participation of local people, it led to the efficient management of forests.

Question 33. What are the various factors that are damaging our forests?
Answer:

• The local people live near forests.
• Industrial needs cause deforestation.
• Development projects like buildings, roads, and dams.
• Damage caused by tourists or the arrangements made for their convenience.

Question 34. The Chipko movement was started in the 1970s in the small village of Garhwal high up in the Himalayas. Villagers stood against greedy contractors. Women folk hugged the trees. Answer the following questions based on the above information:

1. Do you feel inspired by this movement which prevented the felling of trees? Who do you think are the real stakeholders?
2. Which old belief has been challenged by the Chipko movement?
3. What values does the Chipko movement invoke?

Answer:

1. Yes. The local people are the real stakeholders.
2. Chipko movement has challenged the old belief that forests are meant only for timber. Gifts of trees to us are soil, water, and oxygen.
3. Environmental protection, motivation for tree plantation.

Question 35. Today we encounter the problem of water shortage, although it rains well in the rainy season. ‘Khushi Society’ has made a provision for rainwater harvesting.

1. Suggest two methods of rainwater harvesting.
2. How can you store water without any water-borne disease and germs multiplying in it?
3. What values are seen in the members of society?

Answer:

1. Rooftop and underground rainwater harvesting.
2. In closed tanks and underground tanks.
3. Responsible behavior, interaction, and teamwork.

Question 36. Certain NGOs motivate the general public to donate clothes, books, toys, stationery items, utensils, etc., to them. These NGOs further segregate and distribute these items to the needy. Answer the following questions based on the above information:

1. In your opinion what objective objectives are fulfilled by this initiative?
2. What values do they promote?

Answer:

1.

• Good initiative approach to reuse.
• Sensitizing the general public towards the community.

2. Invoking social responsibility among citizens by contributing their share towards generous acts of society towards their underprivileged fellows.

CBSE Class 10 Science Chapter 16 Management Of Natural Resources Multiple Choice Questions

Question 1. From the list given below pick the item that is not a natural resource

1. Soil
2. Water
3. Electricity
4. Air

Answer: 3. Electricity

Question 2. The most rapidly dwindling natural resource in the world is

1. Water
2. Forests
3. Wind
4. Sunlight

Answer: 2. Forests

Question 3. The most appropriate definition ofa natural resource is that it is a substance /commodity that is

1. Present only on land
2. A gift of nature which is very useful to mankind
3. A man-made substance placed in nature
4. Available only in the forest

Answer: 2. A gift of nature which is very useful to mankind

Question 4. The main cause for abundant coliform bacteria in the river Ganga is

1. Disposal of unburnt corpses into water
2. Discharge of effluents from electroplating industries
3. Washing of clothes
4. Immersion of ashes

Answer: 1. Disposal of unburnt corpses into water

Question 5. The pH of the water sample collected from a river was found to be acidic in the range of 3.5-4.S, on the banks of the river were several factories that were discharging effluents into the river. The effluents of which one ofthe following factories is the most likely cause for lowering the pH of river water?

1. Soap and detergent factory
2. Lead battery manufacturing factory
3. Plastic cup manufacturing factory
4. Alcohol distillery

Answer: 2. Lead battery manufacturing factory

Question 6. The range most conducive for the life of freshwater plants and animals is

1. 6.5-7.5
2. 2.0-3.5
3. 3.5 -5.0
4. 9.0-10.5

Answer: 1. 6.5-7.5

Question 7. The three R’s that will help us conserve natural resources for long-term use are

1. Recycle, regenerate, reuse
2. Reduce, regenerate, reuse
3. Reduce, reuse, redistribute
4. Reduce, regenerate, reuse

Answer: 4. Reduce, regenerate, reuse

Question 8. Given below are a few statements related to biodiversity. Pick those that correctly describe the concept of biodiversity

1. Biodiversity refers to the different species of flora and fauna present in an area

2. Biodiversity refers to only the flora ofa given area

3. Biodiversity is greater in a forest

4. Biodiversity refers to the total number of individuals of a particular species living in an area

1. 1 and 2
2. 2 and 3
3. 1 and 3
4. 2 and 3

Answer: 3. 1 and 3

Question 9. Among the statements given below select the ones that correctly describe the concept of sustainable development

1. Planned growth with minimum damage to the environment

2. Growth irrespective ofthe extent of damage caused to the environment

3. Stopping all developmental work to conserve the environment

4. Growth that is acceptable to all the stakeholders

1. 1 and 4
2. 2 and 3
3. 2 and 4
4. 3 only

Answer: 1. 1 and 4

Question 10. In our country, vast tracts of forests are cleared, and a single species of plant is cultivated, This practice promotes

1. Biodiversity in the area
2. Monoculture in the area
3. Growth of natural forest
4. Preserves the natural ecosystem in the area

Answer: 2. Biodiversity in the area

Question 11. A successful forest conservation strategy should involve

1. Protection of animals at the highest trophic level
2. Protection of only consumers
3. Protection ofonly herbivores
4. A comprehensive program to protect all the physical and biological components

Answer: 2. Protection only consumers

Question 12. The important message conveyed by the ‘Cliipko Movement’ is

1. To involve the community in forest conservation efforts
2. To ignore the community in forest conservation efforts
3. To cut down forest trees for developmental activities
4. Government agencies have the unquestionable right to order the destruction of trees in forests

Answer: 1. To involve the community in forest conservation efforts

Question 13. In our country, there are attempts to increase the height of several existing dams like the Tehri and Almati dams across Narmada. Choose the correct statements among the following that are a consequence of raising the height of dams

1. Terrestrial flora and fauna ofthe area are destroyed completely

2. Dislocation of people and domestic animals living in the area

3. Valuable agricultural land may be permanently lost

4. It will generate permanent employment for people

1. 1 and 2
2. 1,2, and 3
3. 2 and 4
4. 1,3, and 4

Answer: 2. 1,2, and 3

Question 14. Expand the abbreviation GAP

1. Governmental Agency for Pollution Control
2. Gross Assimilation by Photosynthesis
3. Ganga Action Plan
4. Governmental Agency for Animal Protection

Answer: 3. Ganga Action Plan

Question 15. Select the incorrect statement

1. Economic development is linked to environmental conservation
2. Sustainable development encourages development for the current generation and conservation of resources for future generations
3. Sustainable development does not consider the viewpoints of stakeholders
4. Sustainable development is a long-planned and persistent development

Answer: 3. Sustainable development does not consider the viewpoints of stakeholders

Question 16. Which ofthe following is not a natural resource?

1. Mango tree
2. Snake
3. Wind
4. Wooden house

Answer: 4. Wooden house

Question 17. Select the wrong statement

1. Forests provide a variety of products
2. Forests have greater diversity
3. Forests do not conserve soil
4. Forests conserve water

Answer: 3. Forests do not conserve soil

Question 18. The Arabari forests of Bengal are dominated by

1. Teak
2. Snake
3. Bamboo
4. Wooden house

Answer: 2. Snake

Question 19. Groundwater will not be depleted due to

1. Afforestation
2. Thermal powerplants
3. Loss of forest, and decreased rainfall
4. Cropping of high water-demanding crops

Answer: 1. Afforestation

Question 20. Opposition to the constitution of large dams is due to

1. Social reasons
2. Economic reasons
3. Environmental reasons
4. All of the above

Answer: 4. All ofthe above

Question 21. Khadins, Bundhis, Ahars, and Kattas are ancient structures that are examples for

1. Grain storage
2. Wood storage
3. Water harvesting
4. Soil conservation

Answer: 3. Water harvesting

Question 22. Pick the right combination of terms which has no fossil fuel.

1. Wind, ocean, and coal
2. Kerosene, wind, and tide
3. Wind, wood, sun
4. Petroleum, wood, sun

Answer: 3. Wind, wood, sun

Question 23. Select the eco-friendly activity among the following:

1. Using a car for transportation
2. Using polybags for shopping
3. Using dyes for colouring clothes
4. Using windmills to generate power for irrigation

Answer: 4. Using windmills to generate power for irrigation

Question 24. It is important to make small check dams across the flooded gullies because they

1. Hold water for irrigation

2. Hold water and prevent soil erosion

3. Recharge groundwater

4. Hold water permanently

1. 1 and 4
2. 2 and 3
3. 3 and 4
4. 2 and 4

Answer: 2.2 and 3

CBSE Class Class 10 Science Chapter 15 Our Environment

Ecosystem

CBSE Class Class 10 Science Chapter 15 Our Environment Definitions

1. The physical and biological world we live in is called the environment.
2.  The physical environment includes soil, water bodies, and air on the surface of the earth. Climatic factors such as sunlight, temperature, rainfall, humidity, pressure, and wind speeds are also considered to be a part of the abiotic environment.
3. The structural and functional system of communities and their environment is called an ecosystem.
4. Man-made ecosystems are called artificial ecosystems.
5. Biodegradable waste materials are those waste materials, which can be broken down into simpler, non-poisonous substances by the action of microorganisms.
6. The waste materials, that cannot be broken down into simpler substances easily in nature, are known as non-biodegradable wastes.
7. Substances that are broken down by the action of bacteria or other saprophytes by the biological process are categorized as biodegradable.
8.  Substances that are not broken down by the action of bacteria or other saprophytes are categorized as non-biodegradable.
9. The materials keep on cycling, i.e., entering into a living system and through death and decay returning to the soil and atmosphere. This process is a bio-geochemical cycle.
10. Biotic environment means living part of the environment.
11. The net-like trophic relationship is called the food web.
12. The food chain starting from the green plants through herbivores to top carnivores is called the grazing food chain.
13. The food chain starts from the dead organic matter being consumed by detritus micro¬organisms which in turn are eaten by some other predators is called detritus food chain.
14.  The relationship between the number of producers and consumers can be represented in a diagrammatic way, which is known as the ecological pyramid.
15. Producers include plants that can make their food. They are also called autotrophs.
16.  Consumers are those organisms that depend on producers for food.
17. Herbivores depending directly on plants are called primary consumers.
18. Carnivores depending on herbivores are called secondary consumers.
19. Decomposers are those organisms that break dead organic materials into simple inorganic substances and during the process derive food and energy from them.
20. The process of concentration of harmful chemicals such as pesticides at each successive step in a food chain is called biological magnification.
21.  Each step of a food chain is called a trophic level.
22.  The series of organisms fixing energy, eating, and being eaten is called a food chain.
23. Parasites are consumers that live on or in other organisms and derive their nourishment from the host body.
24.  One percent of solar energy is fixed by plants.
25. 10% of energy is passed to the next trophic level. This is called the 10% law.
26. The main cause of the depletion of the ozone layer is chlorofluorocarbons (CFCs).
27. The process of reducing the volume of wastes by burning them at temperature is called incineration.

CBSE Class Class 10 Science Chapter 15 Our Environment Short Question And Answers

Question 1. How can you help in reducing the problem of waste disposal? Give any two methods.
Answer:

We can reduce it in the following manner: By reusing some ofthe waste before disposing of it finally in the garbFor example: we can use some plastic containers for storing food articleReducinging the volume wastes by burnt them in the incinerator

Question 2. Accumulation of harmful chemicals in our bodies can be avoided. Explain. How can this be achieved? 
Answer:

1. Crop rotation
2. Bio-fertilizers

Question 3.

1. What percentage of energy available at the producer level is transferred at successive trophic levels in a food chain?
2. What percentage ofthe solar energy is trapped and utilized by the plants?

Answer: 

1. 10%
2. 1%

Question 4. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organ of any trophic level be removed without causing any damage to the ecosystem?
Answer:

Remof allofall the organisms in a trophic level will have different effects on another trophic level. While the number of organisms in the lower trophic level will increase and the number of organisms in the next higher trophic will decrease due to a shortage of food. Organisms of any trophic level cannot be removed without causing any damage to the ecosystem.

Question 5. If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer:

If we generate all the waste as biodegradable the harm will be only for some time, since after some time they will be broken down into simple substances. However, such waste should be removed from residential areas frequently as their accumulation will lead to a foul smell and it will serve as a breeding ground for mosquitos and flies.

Question 6. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer:

The ozone layer at the higher level of atmosphere shields the surface e from the UV UV radiation of the sun. Any damage to this layer will allow. radiation to reach thearth’sth surface. UV radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.

To reduce the damage to the ozone layer United Nations Environment Programme succeeded in forging an agreement to reduce CFC production at the 1986 level

Question 7. Pesticides like DDT which are sprayed to kill pests on crops are found to be present in the soil, groundwater, water bodies, etc. Explain. How do they reach these places?
Answer:

Soil: Pesticides are used to protect plants from insects. They, consequently, get settled into soil particles, when used on plants.

Groundwater: Through irrigation in the fields, these pesticides present in soil pass into lower layers of soil and reach groundwater.

Water bodies wastewater or other agricultural waste is thrown in water bodies like rivers, canals, ponds, etc., the pesticides affect water bodies.

Question 8. State with reason any two possible consequences of the elimination of decomposers from the earth.
Answer:

1. Two possible consequences of the elimination of decomposers from the earth would be as follows:
2. An increase in complex organic substances will cause land and water pollution as well as air pollution.
3. It may disturb the ecosystem as without decomposition, soil will not be replenished, which is essential for ‘plants’ which form the basis ofan ecosystem.

Question 9. Distinguish between biodegradable and non-biodegradable substances. Give two points of difference.
Answer:

1. Biodegradable substances are broken down by microorganisms and replenish the soil.
2. Nonbiodegradable substances do not get broken down by microorganisms, enter the food chain, and cause pollution.

Question 10. What would happen if the number of carnivores decreases in an ecosystem?
Answer:

• The population of herbivores will increase beyond control.
• Autotrophs will disappear from Earth due to overgrazing done by herbivores.
• Both these factors may disturb food chains thus affecting the ecosystem.

Question 11. How are the following caused and what is the effect of each of them on our environment:

1. Depletion of the Ozone layer
2. Acid rain?

Answer:

1. More harmful UV radiation will enter the earth’s atmosphere resulting in diseases like skin cancer in humans.
2. Acid rain corrodes heritage monuments like the Taj Mahal and it also damages crop plants.

Question 12. The food web increases the stability ofan ecosystem. Justify.
Answer:

The food web depicts feeding connections in an ecological community. It consists of many food chains. Thus, if any one organism becomes endangered or extinct, the one who is dependent on it has an alternative option available to him for its survival. In this way, the food web increases stability in an ecosystem.

Question 13. Define producers and consumers and give their examples.
Answer:

Those organisms that can manufacture their food by the process of photosynthesis are termed producers. Examples: Green plants, and algae. Those organisms that consume the food produced, either directly from producers or indirectly by feeding on other consumers are called consumers.

Examples: Fish, snake.

Question 14. Why do food chains generally consist of three or four steps only?
Answer:

1. Since little energy is available for the next level of consumers, food chains generally consist of only three or four steps.
2. The loss of energy at each step is so great that very little usable energy remains after four trophic levels.

Question 15. What is the role of decomposers in the ecosystem?
Answer:

1. Decomposers (fungi and bacteria) help in the recycling of nutrients. They feed on the dead and decaying bodies of plants and animals.
2. They return the nutrients to the soil and thus help in making this ecosystem stable.

Question 16. What will happen if deer is missing in the food chain given below?

Grass →  Deer →  Tiger

1. The population often increases
2. The population of grass decreases
3. Tiger will start eating grass
4. The population of tigers decreases and the population of grasses increases

Answer: 4. The population of tigers decreases and the population of grass increases

Question 17. What are the advantages of cloth bags over plastic bags during shopping?
Answer: Cloth bags are:

1. Capable of carrying more things
2. Made ofbiodegradable material
3. Do not pollute our environment
4. Can be reused

Question 18. What are decomposers? What will be the consequence oftheir absence in an ecosystem?
Answer:

Decomposers break down the complex organic substances of garbage, dead animals, and plants into simpler inorganic substances that go into the soil and are used up again by the plants. In the absence of decomposers, recycling of material in the biosphere will not take place.

CBSE Class Class 10 Science Chapter 15 Our Environment  Multiple Choice Questions

Question 1. Which one ofthe following is an artificial ecosystem?

1. Pond
2. Crop field
3. Lake
4. Forest

Answer: 2. Crop field

Question 2. In a food chain, the third trophic level is always occupied by

1. Carnivores
2. Herbivores
3. Decomposers
4. Producers

Answer: 1. Carnivores

Question 3. An ecosystem includes

1. All living organisms
2. Non-living objects
3. Both living organisms and non-living objects
4. Sometimes living organisms and sometimes non-living objects

Answer: 3. Both living organisms and non-living objects

Question 4. In the given food chain, suppose the amount of energy at the fourth trophic level is 5 kJ, what will be the energy available at the producer level?

Grass – Grasshopper- Frog- Snake Hawk

1. 5 kJ
2. 50 kJ
3. 500kJ
4. 5000 kJ

Answer: 4. 5000 kJ

Question 5. Accumulation of-biodegradable pesticides in a food chain in increasing amounts at each higher trophic level is known as

1. Eutrophication
2. Pollution
3. Biomagnification
4. Accumulation

Answer: 3. Biomagnification

Question 6. Depletion of ozone is mainly due to

1. Chlorofluorocarbon compounds
2. Methane
3. Carbon monoxide
4. Pesticides

Answer: 1. Chlorofluorocarbon compounds

Question 7. Organisms that synthesize carbohydrates from inorganic compounds using radiant energy are called

1. Decomposers
2. Producers
3. Herbivores
4. Carnivores

Answer: 2. Producers

Question 8. In an ecosystem, the 10% of energy available for transfer from one trophic level to the next is in the form of

1. Heat energy
2. Light energy
3. Chemical energy
4. Mechanical energy

Answer: 3. Chemical energy

Question 9. Organisms ofa higher trophic level which feed on several types of organisms belonging to a lower trophic level constitute the

1. Food web
2. Ecological pyramid
3. Ecosystem
4. Food chain

Answer: 1. Food web

Question 10. Flow ofenergy in an ecosystem is always

1. Unidirectional
2. Bidirectional
3. Multidirectional
4. No specific direction

Answer: 1. Unidirectional

Question 11. Excessive exposure of humans to U V-rays results in

1. Damage to immune system

2. Damage to lungs

3. Skin cancer

4. Peptic ulcers

1. 1 and 2
2. 2 and 4
3. 1 and 3
4. 3 and 4

Answer: 3. 1 and 3

Question 12. In the following groups of materials, which group(s) contains only non-biode gradable items?

1. Wood, paper, leather

2. Polythene, detergent, PVC

3. Plastic, detergent, grass

4. Plastic, bakelite, DDT

1. 3
2. 4
3. 1 and 3
4. 2 and 4

Answer: 4. 2 and 4

Question 13. Which ofthe following limits the number of trophic levels in a food chain?

1. Decrease in energy at higher trophic levels
2. Sufficient food supply
3. Polluted air
4. Water

Answer: 1. Decrease in energy at higher trophic levels

Question 14. Which ofthe statements is incorrect?

1. All green plants and blue-green algae are producers
2. Green plants get their food from organic compounds
3. Producers prepare their food from inorganic compounds
4. Plants convert solar energy into chemical energy

Answer: 2. Green plants get their food from organic compounds

Question 15. Which group of organisms are not constituents ofa food chain?

1. Grass, lion, rabbit, wolf
2. Plankton, man, fish, grasshopper
3. Wolf, grass, snake, tiger
4. Frog, snake, eagle, grass, grasshopper

Answer: 3. Wolf, grass, snake, tiger

Question 16. The percentage of solar radiation absorbed by all the green plants for the process of photosynthesis is about

1. 1%
2. 5%
3. 8%
4. 10 %

Answer: 1. 1%

Question 17. In the given figure, the various trophic levels are shown in a pyramid. At which trophic level is maximum energy available?

1. T₄
2. T₂
3. T₁
4. T₃

Answer: 3.

Question 18. Which ofthe following groups contains only biodegradable items?

1. Grass, flowers, and leather
2. Grass, wood, and fruit peels-peels, cake, and lime-juice
3. Cake, wood, and grass.
4. Fruit peels, c,alime juicee-juice

Answer: 4.  Fruit peels, calime juicee-juice

Question 19. Which ofthe following constitutes a food chain?

1. Grass, wheat, and mango
2. Grass, goat, and human
3. Goat, cow, and elephant
4. Grass, fish, and goat.

Answer: 2. Grass, goa,t and human

Question 20. Which ofthe following are environment-friendly practices?

1. Carrying cloth bags to put purchases in while shopping.
2. Switching off unnecessary lights and fans.
3. Walking to school instead of getting your mother to drop you on her scooter.
4. All ofthe above.

Answer:  4. All ofthe above.

Question 21. The decomposers in an ecosystem

1. Convert inorganic material to simpler forms
2. Convert organic materials to inorganic forms
3. Convert inorganic material into organic compounds
4. Do not break organic compounds

Answer: 2. Convert organic materials to inorganic forms

Question 22. If a grasshopper is eaten by a frog, then the energy transfer will be from

1. Producer to decomposer
2. Producer to primary consumer
3. Primary consumer to secondary consumer
4. Secondary consumer to primary consumer

Answer: 3. Primary consumer to secondary consumer

Question 23. Disposable plastic plates should not be used because

1. They are made of material of lightweight weight
2. They are made of toxic materials
3. They are made of biodegradable materials
4. They are made of non-biodegradable materials

Answer: 4. They are made of non-biodegradable materials

CBSE Class 10 Science Chapter 3 Metals And Non-Metals

Elements

1. Metals

Physical Properties of Metals

1.  Strong, hard to cut except Na, K.
2. Malleable, beaten into sheets.
3. Ductile, can be drawn into wires.
4.  Sonorous, produce sound when we strike them.
5. Good conductors of heat and electricity.
6. High melting and boiling points except Na, K

Read and Learn More CBSE Class 10 Science Short Answer Questions

Chemical Properties of Metals

1. React with oxygen to form oxides.
2. Metals can lose electrons to form positive ions.
3. Transition metals show variable valency
   • Example: Cu⁺,Cu²⁺, Fe²⁺, Fe³⁺…………….
4. Except few, metals react with cold water, some with hot, some with steam to form oxides or hydroxides and hydrogen gas.
5. More reactive metals can displace less reactive metals from their salt solution.
6. Metals react with dilute acids to form salt and hydrogen gas except with dil. HNO₃ . They are good which is an oxidising agent.

Exceptional Properties

1. Iron is malleable and strong. It easily rusts in moist air.
2.  Iron is magnetic, and melts at 1530°C.
3. Sodium is so soft, can be cut by a knife. It floats on water, catches fire in the presence of water, and melts at 98°C.
4. Gold is unreactive, highly malleable and ductile and looks attractive.
5. Gold is used in jewellery, and melts at 1064°C.

Mg and Mn react with 5% HNO₃ to produce Hz gas.

6. Al₂O₃. BeO and ZnO are amphoteric (acidic as well as basic) oxides.

7. NO, N₂O, CO or neutral oxides.

2. Metalloids

Composition of Earth’s crust

Most of the metals occur as their compounds except gold, silver, and platinum which occur in free-state

3. Non-metals

Physical Properties of Non-Metals

1. They are brittle.
2. They exist as solids, liquids and gases.
3. They are non-lustrous except for diamond and iodine.
4. They are not conductors of heat and electricity except graphite.
5. Low melting and boiling points except for diamond and graphite.
6. Low density

Chemical Properties of Non-Metals

1. They form acidic oxides.
2.  They gain electrons to form negative ions
3. They are a good oxidising agent. oxidising agents
4. Their oxide dissolves in water forming acids
5. They do not react with dilute acids because they can’t lose electrons
6. More reactive non-metals can displace less reactive non-metals from their salt solution.

CBSE Class 10 Science Chapter 3 Metals And Non-Metals Definitions

1. Metals: Metals are the element which can easily form positive ions by ionising electrons.

For example: Sodium, Potassium, Magnesium, Iron, Copper, etc.

2. Physical characteristics of metals:

1. Conductors of heat and electricity
2. Metals have shining surface
3. Metals have a high tensile strength
4. Metals have sonority

3. Sonority: It is the characteristic ofa metal to emit a deep resonant sound when struck.

4. Tensile strength: It is the resistance of a wire to pull action and is measured by the breaking stress in kilogram per square millimetre.

5. Reactivity of metals: The electropositive character of a metal determines its reactivity.

6. Metallichydrides: The compounds of metals with hydrogen are calledmetallichydrides.

These are usually obtained by passing hydrogen over heated metals.

7. Amphoteric oxides: Such oxides which react with both acids and bases to give salt and water are called amphoteric oxides. For example: A1203, ZnO.

8. Non-metals: Non-metals are the elements which form negative ions by gaining electrons.

9. Physical characteristics of non-metals:

1. Non-metals are brittle.
2. Non-metals are non-ductile.
3. Non-metals have comparatively low melting and boiling points.
4. Non-metals have low densities.

10. Minerals: The metals found in nature in a combined state are called minerals.

11. Ore: An ore is defined as a mineral from which a metal can be extracted economically.

12. Metallurgy: The extraction of a metal from a suitable ore and its refining for use is called metallurgy or metallurgical operations.

13. Calcination: It is the process of heating the concentrated ore in the absence of air

⇒ \(\underset{\text { Zinc carbonate }}{\mathrm{ZnCO}_3(s)} \longrightarrow \underset{\text { Zinc oxide }}{\mathrm{ZnO}(s)}+\underset{\text { Carbon dioxide }}{\mathrm{CO}_2(\mathrm{~g})}\)

14. Roasting: It is the process of heating the ore in the presence of air

⇒ \(2 \mathrm{ZnS}+3 \mathrm{O}_2 \longrightarrow 2 \mathrm{ZnO}+2 \mathrm{SO}_2\)

15. Slag: Some substances when heated with the ore combine with the earthy impurities and form an easily fusible mass. The easily fusible mass is called slag.

16. Gangue:

Ores are associated with earthy or rocky materials as impurities. These impurities are called gangue or matrix.

17. Smelting:

The roasted or calcined ore is mixed with coke and heated in a furnace to obtain free metal. The process of reducing the oxide with coke is called smelting.

18. Electrolysis:

Electrolysis is the process of conduction of electricity through molten or dissolved chemicals to decompose its components.

19. Corrosion: When the surface or metal is attacked by air, water and some other substance, it is said to corrode. The phenomenon is known as corrosion.

20. Galvanisation: The coating of iron with zinc is called galvanisation.

21. Anodising: It is the process of the formation of a thick layer of metal oxide over a metallic object.

22. Alloy: An alloy is a homogeneous mixture of two or more than two metals, which have nearly the same atomic size.

23. Amalgam: It is an alloy of metal with mercury.

24. Aqua regia: The mixture of cones. HCl and cone. HNO in the ratio 3:1.

25. Important chemical reactions of metals

Reaction with oxygen:

Metal + Oxygen Metal oxide

4 Na +O₂ → 2Na₂ O(s)

4K+ O₂ → 2K₂O(s)

2Cu +O₂→ (heat) 2CuO(s)

4Al +3O₂→(heat) 2AlO(s)

2 Zn +3O₂→(heat) →2 ZnO(s)

4 Fe +3O→(heat)→2 Fe₂O₃(s)

2 Mg +O₂ → (heat) 2MgO(s)

2 Ca +O₂ →(heat)→ 2CaO(s)

Reaction with water

Metal + Water Metal Oxide + Hydrogen or hydroxide

2Na + 2H₂O→(cold)→ 2NaOH + H₂

2K + 2H₂O→(cold) →2KOH + H₂

Ca + 2H₂O→(cold)→ Ca(OH)₂ + H₂

Mg + 2H₂O→(hot)→ Mg(OH)₂ + H₂

2Al + 3H₂O→(steam)→Al₂O₃ + 3H₂

3Fe + 4H₂O→(steam)→ Fe₃O₄ + H₂

Reaction with dil acid

Metal + dil acid→ Salt + Hydrogen

Zn + 2HCl(dil)→ Salt + Hydrogen

Mg + H₂SO₄(dil)→ MgSO₄ + H₂

Mg + 2HNO₃→(5%) →Mg(NO₃)₂ + H₂

Mn + 2HNO₃→ (5%)→ Mn(NO₃)₂ + H₂

2Al + 6HCl → 2AlCl₃ + 3H₂

The metal reacts with salts

More reactive metal + salt → Salt + Less reactive metal

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

Mg(s)+FeSO(aq) → MgSO₄(aq) + Fe(s)

Zn(s) + FeSO₄(aq) → ZnSO₄(aq) + Fe(s)

2Al(s) + 3CuSO₄(aq) → Al₂(SO₄)₃(aq) + 3Cu

Mg(s) + CuSO₄(aq) → MgSO₄(aq) + Cu(s)

Cu +2Ag NO₃(aq)→ Ag +Cu(NO₃)₂

Ag + Cy (NO₃)₂ → No reaction

Metal oxide reaction with water

Metal oxide + water Metal hydroxide

K₂O+H₂O →2KOH

CaO+H₂O→Ca(OH)₂

MgO+H₂O→Mg(OH)

NaO +HO → 2NaOH

Metal oxide reacts with acid

Metallic oxide + Acids → Salt + Water

Salt + Water MgCl +However

ZnO + 2HCl(dil) → ZnCl₂ + H₂O

CuO + H₂SO₄(dil) →CuSO₄ + H₂O

FeO + H₂SO₄(dil)→ FeSO₄ + H₂O

Al₂O₃ + 6HCl→ Al₂Cl₂ + 3H₂O

26. Important chemical properties of metals

Reaction with oxygen

Non-metals + Oxygen Non-metal oxide (acidic oxide)

S + O₂  → SO₂ 

c + O₂  →CO₂ 

4P + 5O₂  → 2P₂O₆, NO, CO and NO are neutral oxides

4B +3O₂ → BO

Si +O₂  →  SiO₂ 

Non-metallic oxides react with water

Non-metallic oxide + water→ Acids

CO₂  + H₂O H₂CO₃ (Carbonic acid)

SO₂ + H₂O→ H₂CO₃ (Carbonic acid)

SO₃ + H₂O→ H₂SO₄ (Sulphuric acid)

P₂O₅ + 3H₂O→ 2H₃PO₄ (Phosphoric acid)

B₂O₃+ 3H₂O → 2H₃PO₄ (Phosphoric acid)

SiO₂ + H₂O → H₂SiO₃ (Silicic acid)

H₂SiO₃(Silicic acid)

Acidic oxides + Base Salt + Water

CO₂ + 2NaOH → Na₂CO₃+H₂O

CO₂ + Ca(OH)₂ → Na₂CO₃+H₂O

SO₂ + 2NaOH → Na₂SO₃ + H₂O

More reactive non-metals react with salt

More reactive non-metal + Salt → Salt+ Less reactive non-metal

More reactive non-metal + Salt

Cl₂ + 2KBr→ 2KCl + Br₂

Cl₂ + 2KI → Cl₂+ 2KI

Br₂ + 2KI →2KBr + I₂

Order of reactivity: Cl₂ > Br₂ > I₂

Order of reactivity: Cl₂ > Br₂ > I₂

Extraction of metals from ores

Alloys:

Homogeneous mixture of two or more metals which have better properties than metals. One of them can be non-metal also. Steel is an alloy of iron and carbon. It does not get rusted.

Important Alloys:

1. Stainless steel: It is an alloy of Fe. C. nickel and chromium which is hard, malleable and does not rust, It is used for utensils and surgical instruments.

2. Brass: It is an alloy of copper and zinc. It is used to make decorative articles

3. Bronze: It is an alloy of copper and tin. It’s used for medals and statues.

4. Solder is an alloy of an alloy of It is used for soldering purpose

5. Duralumin: Duralumin is an alloy of Alandmagnesium.It is used to make the body of the aeroplane

6. 24-carat gold is pure gold. It is very soft. It is alloyed with copper and silver to make it hard to make jewellery of 22-carat gold=\(\frac{22}{24} \times 100\)

= 91.6% pure

7. Al is used for transmission wires, cooking foil, drink cans, and coating CDs and DVDs. Aluminium powder is used In silver paints. Al is used as a reducing agent. Al Is used for making utensils and pressure cooker

Relative Reactivities of Metals

CBSE Class 10 Science Chapter 3 Metals And Non-Metals Short Question And Answers

Question 1. Give an example of a metal which

1. Is a liquid at room temperature.
2. Can be easily cut with a knife.
3. Is the best conductor of heat.
4. Is a poor conductor of heat.

Answer:

1. Mercury is a liquid at room temperature.
2. Sodium can be easily cut with a knife.
3. Silver is the best conductor of heat.
4. Lead is a poor conductor of heat.

Question 2. Explain the meanings of malleable and ductile.
Answer:

When a metal can be beaten into thin sheets with a hammer, the metal is called malleable and the property is called malleability. When a metal can be drawn into thin wires, the metal is called ductile and the property is called ductility.

Question 3. Write equations for the reactions of

1. Iron with steam
2. Calcium and potassium in water

Answer:

1. \(\underset{\text { Iron }}{3 \mathrm{Fe}(s)}+\underset{\text { Water }}{4 \mathrm{H}_2 \mathrm{O}(l)} \longrightarrow \underset{\text { oxide of iron }}{\mathrm{Fe}_3 \mathrm{O}_4(s)}+\underset{\text { Hydrogen }}{4 \mathrm{H}_2(g)}\)

2.

Question 4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H₂SO₄
Answer:

Hydrogen gas is produced when dilute hydrochloric acid is added to a reactive metal.

Reaction of iron with dilute sulphuric acid

⇒ \(\underset{\text { Iron }}{\mathrm{Fe}}+\underset{\text { Sulphuric acid }}{\mathrm{H}_2 \mathrm{SO}_4(\alpha q)} \longrightarrow \underset{\text { Ferrous sulphate }}{\mathrm{FeSO}_4(\alpha q)}+\underset{\text { Water }}{\mathrm{H}_2 \mathrm{O}}\)

Question 5. What would you observe when zinc is added to a solution of iron (2) sulphate? Write the chemical reaction that takes place.
Answer:

Zinc is more reactive than iron. When zinc is added to a solution of iron (2) sulphate, the green colour of iron (2) sulphate fades out and iron metal is deposited.

Zn(s)(zinc) + FeSO₄(aq)(Iron sulphate) → Fe(Iron)] +ZnSO(aq)(Zinc sulphate)

Question 6. Why do ionic compounds have high melting points?
Answer:

Ionic compounds do not exist as single molecules but exist as aggregates of a large number of positive and negative ions due to strong electrostatic forces. Thus, a large amount of energy is required to break the inter-ionic attraction, hence these have high melting points

Question 7. What are alloys?
Answer:

An alloy is a homogeneous mixture of two or more metals or a metal and a non-metal. It is prepared by first melting the main metal, and then dissolving the required amount of other metals or non-metals. The mixture is then cooled to room temperature to form an alloy of a given composition.

Question 8. What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer:

Those oxides which react with both acids as well as bases to produce salt and water are known as amphoteric oxides. Two examples of amphoteric oxides are Aluminium oxide (Al₂O₃) and zinc oxide (ZnO).

Question 9. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Answer:

In electrolytic refining of a metal M, the impure metal M is made the anode and a thin strip of pure metal M is made the cathode. A solution of the metal M salt is used as an electrolyte.

For Example:

For refining copper metal, the strip of the pure metal would be made cathode, and that of impure metal would be made anode and the electrolyte would be copper sulphate solution.

Question 10. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
Answer:

When the copper vessel is kept in moist air, it reacts with moist carbon dioxide in the air to form a green substance. The green substance is copper carbonate, which is basic. When it is treated with lemon or tamarind juice containing acid, neutralisation of the base occurs which cleans the vessel.

Question 11. Name two metals which are purified by electrolytic refining. Mention the anode, cathode and the electrolyte used in the refining process. At which electrode would the pure metal be deposited?
Answer: 

Copper, zinc.

Impure metal is made of anode and a thin strip of pure metal is made of cathode. A solution of the metal salt is used as an electrolyte. Pure metal from the electrolyte is deposited on the cathode.

Question 12. Write the electron dot structure for sodium and chlorine atoms. How do these form a chemical bond? Name the type of bond so formed. Why does a compound so formed have a high melting point?
Answer:

The electron dot diagrams of Na and Cl are as follows:

• They form bonds by the transfer of an electron. Na loses one electron to form Na⁺ ion whereas Cl gains one electron to form Cl^– ion.
• The bond formed is an ionic or electrovalent bond.
• The compound (NaCl) thus formed has a high melting point due to the strong force of attraction between Na⁺ and Cl^– ion.

Question 13. Mention the names of the metals for the following

1. Two metals are alloyed with iron to make stainless steel.
2. Two metals are used to make jewellery.

Answer:

1. Nickel and chromium
2. Gold and platinum

Question 14. Write one example of each of

1. A metal which is so soft that, it can be cut with a knife and a non-metal which is the hardest substance.
2. A metal and a non-metal exist as a liquid at room temperature.

Answer:

1. Sodium, carbon (diamond)
2. Mercury is a liquid metal, bromine is a liquid non-metal.

Question 15. A student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and a green coating on copper coins. State the chemical name of the black and green coating. How are they formed?
Answer:

Black coating: Silver sulphide (Ag₂S)

Green coating: Basic copper carbonate [CuCO₃.Cu(OH)₂]

The action of

1. HS or sulphur compounds are present in the atmosphere.
2. Carbon dioxide, oxygen and water vapour are present in the atmosphere.

Question 16.

1. Write the electron dot structures for potassium and chlorine.
2. Show the formation of KCl by the transfer of electrons.
3. Name the ions present in this compound, KCl.

Answer:

3. KCl has K⁺ and Cl^–.

Question 17. Explain the formation of the ionic compound CaO with an electron dot structure. An atomic number of calcium and oxygen are 20 and 8 respectively.

Name the constituent metals of bronze.

Answer:

⇒ \(\underset{2,8,8,2}{\mathrm{Ca}} \longrightarrow \mathrm{Ca}^{2+}+\underset{2,8,8}{2 \mathrm{e}^{-}}\)

⇒ \(\underset{2,6}{\mathrm{O}}+2 \mathrm{e}^{-} \longrightarrow \underset{2,8}{\mathrm{O}^{2-}}\)

Bronze is made up of copper and tin.

Question 18. Out of the two metals P and Q, P is less reactive than Q. Suggest an activity to arrange these metals in the order of their decreasing reactivity. Support your answer with a suitable chemical equation.
Answer:

Activity: In a test tube, a small amount of salt solution of P is taken and metal Q is added to it. Q being more reactive, displaces metal P from its salt solution.

Chemical equation:

Metal Q + Salt solution of P → Salt solution of Q + Metal P.

Question 19. Define an alloy. How is an alloy prepared?
Answer:

A homogeneous mixture of two or more metals or a metal and a non-metal is known as an alloy. It is prepared by first melting the primary metal, and then, dissolving the other elements in it in definite proportions.

Question 20. A compound ‘Z’ is formed by the transfer of electrons from a metal ‘X’ to a non-metal Y. Identify the type of bond formed in the compound. List three general properties of the compounds formed by such types of bonds.
Answer:

Ionic compounds are formed in these compounds.

The general properties of ionic compounds are:

1. Solid
2. High melting and boiling point
3. Soluble in water
4. Good conductor of electricity

Question 21. Give reasons for the following:

1. School bells are made up of metals.
2. Electrical wires are made up of copper.

Answer:

Because metals are sonorous.

Copper is a very good conductor of electricity.

Question 22.

1. Name a metal which does not stick to glass.
2. Name the metal which is commonly used in thermite welding.
3. What is the nature of zinc oxide?

Answer:

1. Hg (Mercury)
2. Al (Aluminium)
3. Basic

Question 23. Describe ionic compounds based on the following properties:

1. A strong force of attraction between positive and negative ions
2. Solubility of compounds in water
3. Electrical conductivity

Answer:

Owing to the strong force of attraction between the positive and negative ions, ionic compounds are solids.

• These compounds are generally brittle and break into pieces when pressure is applied.
• Ionic compounds are generally soluble in water.
• Ionic compounds in the solid state do not conduct electricity but in aqueous and molten states, they do conduct electricity.

Question 24.

1. ‘Sodium is a highly reactive metal and it cannot be obtained from its oxide by heating with carbon’. Give reason.
2. How can sodium be obtained from sodium chloride?

Answer:

Sodium cannot be obtained from its oxide by heating with carbon because carbon cannot reduce the oxides of sodium.

Sodium can be obtained from sodium chloride by the process of electrolytic reduction.

Question 25. Define the term ‘anode mud. Name the electrode made of pure metal. State the reactions taking place at the cathode and at the anode during the electrolytic refining of copper.
Answer:

The insoluble impurities which settle down at the bottom of the anode are known as anode mud.

The cathode is made of pure metal.

At anode: \(\mathrm{Cu}(s) \longrightarrow \mathrm{Cu}^{2+}(a q)+2 e^{-}\)

At cathode: \(\mathrm{Cu}^{2+}(a q)+2 e^{-} \longrightarrow \mathrm{Cu}(s)\)

Question 26. Name the following:

1. A metal, which is preserved in kerosene.
2. A lustrous coloured non-metal.
3. A metal, which can melt while kept on the palm.
4. A metal, which is a poor conductor of heat.

Answer:

1. Sodium is preserved in kerosene.
2. Iodine is a lustrous coloured non-metal.
3. Gallium or caesium
4. Lead or mercury

Question 27. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer:

It is because of the following reasons:

1. Copper does not react with hot water or steam, whereas steel reacts with steam.
2. Copper is one of the best conductors of heat as compared to steel.
3. Copper has a high melting point as compared to steel.

Question 28. Write chemical equations that show aluminium oxide reacts with acid as well as base.
Answer:

⇒ \(\mathrm{Al}_2 \mathrm{O}_3+6 \mathrm{HCl} \longrightarrow 2 \mathrm{AlCl}_3+3 \mathrm{H}_2 \mathrm{O}\)

⇒  \(\mathrm{Al}_2 \mathrm{O}_3+2 \mathrm{NaOH} \longrightarrow 2 \mathrm{NaAlO}_2+\mathrm{H}_2 \mathrm{O}\)

Question 29. Explain why calcium metal after reacting with water starts floating on its surface. Write the chemical equation for the reaction. Name one more metal that starts floating after some time when immersed in water.
Answer:

Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal.

⇒  \(\mathrm{Ca}(\mathrm{s})+2 \mathrm{H}_2 \mathrm{O}(\mathrm{l}) \longrightarrow \mathrm{Ca}(\mathrm{OH})_2+\mathrm{H}_2(\mathrm{~g})\)

Magnesium reacts with hot water and starts floating due to the bubbles of hydrogen gas sticking to its surface.

Question 30. Why is it that non-metals do not displace hydrogen from dilute acids?
Answer: Those oxides which are both acidic as well as basic are called amphoteric oxides

Example: Al₂O₃, ZnO.

This is because non-metals do not supply electrons to change H+ ions into hydrogen gas.

Question 31. During the extraction of metals, electrolytic refining is used to obtain pure metals.

1. Which material will be used as anode and cathode for refining silver metal by this process?
2. Suggest a suitable electrolyte also.
3. In this electrolytic cell, where do we get pure silver after passing an electric current?

Answer:

1. Anode : Impure silver

Cathode: Pure silver

2. Electrolyte: Silver salt, such as AgNO3, AgCl, etc.

3. We get pure silver at the cathode

Question 32. Compound X and aluminium are used to join railway tracks.

1. Identify the compound X
2. Name the reaction
3. Write down its reaction.

Answer:

Compound X must be iron (3) oxide, Fe₂O₃

The reaction is known as the ‘thermite reaction’ or ‘alumino thermy’.

The reaction is carried out by igniting the mixture with a Mg-ribbon.

Question 33. When a metal X is treated with cold water, it gives a basic salt Y with the molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y, and Z and also write the reaction involved.
Answer:

The base with molecular mass 40 is NaOH.

Hence, the metal X be sodium (Na). It reacts with H₂O to form the base NaOH and liberates H₂ gas which easily catches fire

Question 34. A non-metal X exists in two different forms Y and Z. Y is the hardest natural substance, whereas Z is a good conductor of electricity. Identify X, Y and Z.
Answer: 

Non-metal ‘X’ must be carbon. It exists in two forms, diamond and graphite.

Diamond is the hardest natural substance. Hence, ‘Y’ is a diamond.

Graphite is a good conductor of electricity. Hence, ‘Z’ is graphite.

Question 35. The following reaction takes place when aluminium powder is heated with MnO₂

⇒ \(3 \mathrm{MnO}_2(s)+4 \mathrm{Al}(s) \longrightarrow 3 \mathrm{Mn}(l)+2 \mathrm{Al}_2 \mathrm{O}_3(l)+\text { Heat }\)

1. Is aluminium getting reduced?
2. Is MnO₂ getting oxidised?

Answer:

1. No, because oxygen is added to aluminium, so it is getting oxidised
2. No, since manganese has lost oxygen, therefore it is getting reduced.

Question 36. A metal A, which is used in the thermite process, when heated with oxygen gives an oxide B, which is amphoteric. Identify A and B. Write down the reactions of oxide B with HCl and NaOH.
Answer:

A = Aluminium

B = Al₂O₃

Question 37. A metal that exists as a liquid at room temperature is obtained by heating its sulphide in the presence of air. Identify the metal and its ore and give the reaction involved.
Answer:

The metal that exists as a liquid at room temperature is mercury (Hg). It is obtained by heating its sulphide ore, HgS, called ‘cinnabar’ in the presence of air (roasting). The metal sulphide is first converted into metal oxide (HgO) which on further heating is reduced to Hg.

Question 38. Give the formulae of the stable binary compounds that would be formed by the combination of the following pairs of elements.

1. Mg and N₂
2. Li and O₂
3. Al and Cl₂
4. K and O₂

Answer:

1. Mg₃N₂
2. Li₂O
3. AlCl₂
4. K₂O

Question 39. A non-metal A is an important constituent of our food and forms two oxides B and C. Oxide B is toxic whereas C causes global warming.

1. Identity A, B, and C
2. To which Group of the Periodic Table does A belong?

Answer:

1. A carbon, B = carbon monoxide (CO) C = Carbon dioxide (CO₂)
2. Carbon (A) belongs to group 14 of the periodic table.

Question 40. Name one metal and one non-metal that exist in a liquid state at room temperature. Also, name two metals having melting point less than 310 K (37°C).
Answer:

Metal existing in a liquid state at room temperature is mercury and non-metal is bromine.

The metals with melting points less than 310 K are caesium (Cs) and Gallium (Ga).

Question 41. Using the electronic configurations, explain how the magnesium atom combines with the oxygen atom to form magnesium oxide by transfer of electrons.
Answer:

The atomic number of magnesium

⇒ \(\underset{2,8,2}{\mathrm{Mg}} \longrightarrow \underset{2,8}{\mathrm{Mg}^{2+}+2 \mathrm{e}^{-}}\)

The atomic number of oxygen = 8

⇒  \(\underset{2,6}{\mathrm{O}}+2 \mathrm{e}^{-} \longrightarrow \underset{2,8}{\mathrm{O}^{2-}}\)

Question 42. List three properties of sodium in which it differs from the general physical properties of
most metals.
Answer:

It has low density.

It has a low melting point.

Sodium is so soft that it can be cut with a knife.

Question 43. What happens when

1. ZnCO₃ is heated in the absence of oxygen.
2. A mixture of Cu₂O and CuS is heated.

Answer:

Question 44. An element A reacts with water to form compound B which is used in whitewashing. The compound B on heating forms an oxide C which on treatment with water gives back B. Identify A, B, and C and give the reactions involved.
Answer:

A = Ca; B = Ca (OH)₂ ; C = CaO

Question 45. A metal M does not liberate hydrogen from acids but reacts with oxygen to give a black-coloured product. Identify M and black coloured product and also explain the reaction of M with oxygen.
Answer:

Cu + HCl/H₂SO₄/HNO₃→ No H₂ is evolved

2 Cu(s)+O₂(g)→  (Heat) →  2CuO(s) Copper(2)oxide (Black product)

Question 46. A solution of CuSO₄ was kept in an iron pot. After a few days, the iron pot was found to have several holes in it. Explain the reason in terms of reactivity. Write the equation of the reaction involved.
Answer:

Fe is more reactive than Cu and hence displaces Cu from CuSO, solution. The following reaction takes place:

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

Question 47. Of the three metals X, Y, and Z. X reacts with cold water, Y with hot water and Z with steam only. Identify X, Y, and Z and also arrange them in order of increasing reactivity.
Answer:

X = Na or K, Y = Mg, Z = Fe.

Increasing reactivity: Na/K > Mg > Fe.

Question 48. Element A burns with a golden flame in the air. It reacts with another element B, atomic number 17 to give a product C. An aqueous solution of product C on electrolysis gives a compound D and liberates hydrogen. Identify A, B, C, and D. Also write down the equations for the reactions involved.
Answer:

A Sodium, B = chlorine and, C = Sodium chloride

2 Na(s) + Cl₂(g) → 2NaCl(s)

D = Sodium hydroxide

2 Na⁺Cl^–(aq) +2H₂O(l) →  (Electrolysis) → 2NaOH(aq)+Cl₂(g) +H₂(g)

Question 49. Two ores A and B were taken. On heating ore A gives CO, whereas, ore B gives SO What steps will you take to convert them into metals?
Answer:

Since ore A gives CO₂, and ore B gives SO₂. Therefore, ores are MCO and MS.

A can be obtained

MCO₃ →  MO+CO₂

MO+C  → M+ CO

Question 50. What happens when

1. ZnCO₃ is heated in the absence of oxygen.
2. A mixture of Cu₂O and Cu₂S is heated.

Answer:

ZnCO₃→ ZnO+CO₂↑

2Cu₂O+Cu₂S→6Cu+SO₂↑

Question 51. When a metal X is treated with cold water, it gives a basic Y with the molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y and Z and also write the reaction involved.
Answer:

X Sodium, Y = NaOH, Z = H₂ ↑

2 Na + 2H₂O → 2NaOH (aq) + H₂(↑)

Question 52. Give the formulae of the stable binary compounds that would be formed by the combination of the following pairs of elements.
Answer:

1. Mg, N₂
2. LiO₂
3. AlCl₃
4. K₂O

Question 53. A metal ‘E’ is stored under kerosene oil. When a small piece of it is left open in the air, it catches fire. When the product formed is dissolved in water it turns red litmus blue.

Name the metal E.

Write the chemical equation for the reaction when it is exposed to air and when the product is dissolved in water.

CBSE Class 10 Science Chapter 3 Metals And Non-Metals Multiple Choice Questions

Question 1. Which of the following properties is generally not shown by metals?

1. Electrical conduction
2. Sonorous in nature
3. Dullness
4. Ductility

Answer: 3. Dullness

Question 2. The ability of metals to be drawn into thin wire is known as

1. Ductility
2. Malleability
3. Sonorosity
4. Conductivity

Answer: 1.  Malleability

Question 3. Aluminium is used for making cooking utensils. Which of the following properties of aluminium are responsible for the same?

1. Good thermal conductivity

2. Good electrical conductivity

3. Ductility

4. High melting point

1. 1 and 2
2. 1 and 3
3. 2 and 3
4. 1 and 4

Answer: 4.  1 and 4

Question 4. Which one of the following metals does not react with cold as well as hot water?

1. Na
2. Ca
3. Mg
4. Fe

Answer: 4.  Fe

Question 5. Which of the following oxide(s) of iron would be obtained on the prolonged reaction of iron with steam?

1. FeO
2. Fe₂O₃
3. Fe₃O₄
4. Fe₂O₃ and Fe₂O₄

Answer: 3.  Fe₃O₄

Question 6. What happens when calcium is treated with water?

1. It does not react with water

2. It reacts violently with water

3. It reacts less violently with water

4. Bubbles of hydrogen gas formed stick to the surface of calcium

1. 1 and 4
2. 2 and 3
3. 1 and 2
4. 3 and 4

Answer: 4.  3 and 4

Question 7. Generally, metals react with acids to give salt and hydrogen gas. Which of the following acids does not give hydrogen gas on reacting with metals (except Mn and Mg)?

1. H₂SO₄
2. HCl
3. HNO₃
4. All of these

Answer: 3. HNO₃

Question 8. The composition of aqua-regia is

1. \(\begin{array}{cll}
\text { Dil. } \mathrm{HCl} & : & \text { Conc. } \mathrm{HNO}_3 \\
3 & : & 1
\end{array}\)

2. \(\begin{array}{cll}
\text { Conc. } \mathrm{HCl} & : & \text { Dil. } \mathrm{HNO}_3 \\
3  : & 1
\end{array}\)

3. Conc.HCl (3): Conc.HNO₃(1)

4. \(\begin{array}{cll}
\text { Dil. } \mathrm{HCl} & : & \text { Conc. } \mathrm{HNO}_3 \\
3 & : & 1
\end{array}\)

Answer: 3. Conc.HCl (3): Conc.HNO₃(1)

Question 9. Which of the following are not ionic compounds?

1. KCl

2. HCl

3. CCl₄

4. NaCl

1. 1 and 2
2. 2 and 3
3. 3 and 4
4. 1 and 3

Answer: 2. HCl

Question 10. Which one of the following properties is not generally exhibited by ionic compounds?

1. Solubility in water
2. Electrical conductivity in solid state
3. High melting and boiling points
4. Electrical conductivity in molten state

Answer:  2. Electrical conductivity in solid state

Question 11. Which of the following metals exists in their native state in nature?

1. Cu

2. Au

3. Zn

4. Ag

1. 1 and 2
2. 1 and 3
3. 2 and 4
4. 3 and 4

Answer: 3. Zn

Question 12. Metals are refined by using different methods. Which of the following metals are refined by electrolytic refining?

1. Au

2. Cu

3. Na

4. K

1. 1 and 2
2. 1 and 3
3. 2 and 3
4. 3 and 4

Answer: 1. Au

Question 13. Silver articles become black on prolonged exposure to air. This is due to the formation of

1. Ag₃N
2. Ag₂O
3. Ag₂S
4. Ag₂S and Ag₂N

Answer: 3. Ag₂S

Question 14. Galvanisation is a method of protecting iron from rusting by coating with a thin layer of

1. Galium
2. Aluminium
3. Zinc
4. Silver

Answer: 3. Galium

Question 15. Stainless steel is a very useful material for our life. In stainless steel, iron is mixed with

1. Ni and Cr
2. Cu and Cr
3. Ni and Cu
4. Cu and Au

Answer: 1. Ni and Cr

Question 16. If copper is kept open in the air, it slowly loses its shining brown surface and gains a green coating. It is due to the formation of

1. CuSO₄
2. CuCO₃
3. Cu(NO₃)₂
4. CuO

Answer: 2.  CuCO₃

Question 17. Generally, metals are solid. Which one of the following metals is found in a liquid state at room temperature?

1. Na
2. Fe
3. Cr
4. Hg

Answer:  4. Hg

Question 18. Which of the following metals are obtained by electrolysis of their chlorides in a molten state?

1. Na

2. Ca

3. Fe

4. Cu

1. 1 and 4
2. 3 and 4
3. 1 and 3
4. 1 and 2

Answer: 4. 1 and 2

Question 19. Generally, non-metals are not lustrous. Which of the following non-metal is lustrous?

1. Sulphur
2. Oxygen
3. Nitrogen
4. Iodine

Answer: 4. Iodine

Question 20. Which one of the following four metals would be displaced from the solution of its salts by the other three metals?

1. Mg
2. Ag
3. Zn
4. Cu

Answer: 2. Ag

Question 21. 2 ml each of concentrated HCL, HNO, and a mixture of concentrated HCl and concentrated HNO, in the ratio of 3: 1 were taken in test tubes labelled as A, B, and C.  A small piece of metal was put in each test tube. No change occurred in test tubes A and B but the metal got dissolved in test tube C respectively. The metal could be

1. Al
2. Au
3. Cu
4. Pt

Answer: 2. Au

Question 22. An alloy is

1. An element
2. A compound
3. A homogeneous mixture
4. A heterogeneous mixture

Answer: 3. A homogeneous mixture

Question 23. An electrolytic cell consists of

1. Positively charged cathode

2. Negatively charged anode

3. Positively charged anode

4. Negatively charged anode

1. 1 and 2
2. 3 and 4
3. 1 and 3
4. 2 and 4

Answer:  2. 3 and 4

Question 24. During electrolytic refining of zinc, it gets

1. Deposited on cathode
2. Deposited on anode
3. Deposited on the cathode as well as anode
4. Remains in the solution

Answer: 1. Deposited on cathode

Question 25. An element A is soft and can be cut with a knife. This is very reactive to air and cannot be kept open in air. It reacts vigorously with water. Identify the element from the following

1. Mg
2. Na
3. P
4. Ca

Answer: 2.  Na

Question 26. Alloys are homogeneous mixtures of a metal with a metal or non-metal. Which among the following alloys contain non-metal as one of its constituents?

1. Brass
2. Bronze
3. Amalgam
4. Steel

Answer: 4.  Steel

Question 27. Which among the following statements is incorrect for magnesium metal?

1. It burns in oxygen with a dazzling white flame
2. It reacts with cold water to form magnesium oxide and evolves into hydrogen gas
3. It reacts with hot water to form magnesium hydroxide and evolves hydrogen gas
4. It reacts with steam to form magnesium hydroxide and evolves hydrogen gas

Answer: 2. It reacts with cold water to form magnesium oxide and evolves into hydrogen gas

Question 28. Which among the following alloys contain mercury as one of its constituents?

1. Stainless steel
2. Alnico
3. Solder
4. Zinc amalgam

Answer: 4.  Zinc amalgam

Question 29. The reaction between X and Y, forms compound Z. X loses electrons and Y gains electrons. Which of the following properties is not shown by Z?

1. Has a high melting point
2. Has a low melting point
3. Conducts electricity in a molten state
4. Occurs as solid

Answer: 2. Has a low melting point

Question 30. The electronic configurations of three elements X, Y, and Z are X-2, 8; Y – 2, 8, 7 and Z-2, 8, 2. Which of the following is correct?

1. X is a metal
2. Y is a metal
3. Z is a non-metal
4. Y is a non-metal and Z is a metal

Answer: 4. Y is a non-metal and Z is a metal

Question 31. Although metals form basic oxides, which of the following metals form an amphoteric oxide?

1. Na
2. Ca
3. Al
4. Cu

Answer: 3. Al

Question 32. Generally, non-metals are not conductors of electricity. Which of the following is a good conductor of electricity?

1. Diamond
2. Graphite
3. Sulphur
4. Fullerene

Answer: 2. Graphite

Question 33. Electrical wires have a coating of an insulating material. The material generally used is

1. Sulphur
2. Graphite
3. PVC
4. All can be used

Answer: 3. PVC

Question 34. Which of the following non-metals is a liquid?

1. Carbon
2. Bromine
3. Phosphorus
4. Sulphur

Answer: 2. Bromine

Question 35. Which of the following can undergo a chemical reaction?

1. MgSO₄ + Fe
2. ZnSO₄+ Fe
3. MgSO₄ + Pb
4. CuSO₄+ Fe

Answer: 4.  CuSO₄+ Fe

Question 36. Which one of the following figures correctly describes the process of electrolytic refining?

Answer: 3.

Question 37. Which of the following pairs will give displacement reactions?

1. NaCl solution and copper metal
2. MgCl₂, solution and aluminium metal
3. FeSO₄ solution and silver metal
4. AgNO₃, solution and copper metal

Answer: 4. AgNO₃, solution and copper metal

Question 38. Which of the following methods is suitable for preventing an iron frying pan from rusting?

1. Applying grease
2. Applying paint
3. Applying a coating of zinc
4. All of the above

Answer:  4.  All of the above

Question 39. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be

1. Calcium
2. Carbon
3. Silicon
4. Iron

Answer: 1. Calcium

Question 40. Food cans are coated with tin and not with zinc because

1. Zinc is costlier than tin.
2. Zinc has a higher melting point than tin.
3. Zinc is more reactive than tin.
4. Zinc is less reactive than tin.

Answer: 3. Zinc is more reactive than tin.

CBSE Class 10 Science Chapter 2 Acids And Bases And Salts

Salts:

Indicators:

CBSE Class 10 Science Chapter 2 Acids And Bases And Salts Definitions

1. Acids: Acids are sour and change the colour of blue litmus to red.

Examples of Acids:

Hydrochloric acid: HCI

Sulphuric acid: H₂SO₄

Nitric acid: HNO₃

Acetic acid: CH₃COOH

Phosphoric acid: H₃PO₄

Read and Learn More CBSE Class 10 Science Short Answer Questions

2. Properties of an Acidic Solution:

1. Tastes sour.
2. Reacts with metals such as zinc, magnesium, etc. liberating hydrogen gas.
3. Changes the colour of litmus from blue to red.
4. Conducts electricity.

3. Bases: Bases are bitter and change the colour of red litmus to blue

Examples of Bases:

Sodium hydroxide: NaOH

Potassium hydroxide: KOH

Ammonium hydroxide: NH₄OH

Calcium hydroxide : Ca(OH)₂

Barium hydroxide : Ba(OH)₂

4. Properties of a Basic Solution:

1. Tastes bitter, and feels slippery.
2. Reacts with an acidic solution to neutralize the properties or characteristics of an acid.
3. Changes the colour of litmus from red to blue.
4. Conducts electricity.

5. Indicators:

Indicators are chemical substances which give different colours in acidic or basic solutions.

6. Olfactory indicators:

The substances which have different odours in acid and base solution. For example, vanilla essence has a characteristic pleasant-smelling acid solution and no smell in an alkali solution.

7. Reaction of acids with metals:

Acid + Metal→ Salt + Hydrogen gas

H₂SO₄(aq) + Zn(s)→ ZnSO₄(aq) + H₂(g)

8. Reaction of bases with metals:

Base + Metal→ Salt + Hydrogen

2NaOH + Zn→ Na₂ZnO₂+ H₂

9. Reaction of Acids with metal Carbonates:

Acid + Metal Carbonate→ Salt + CO₂ + H₂O

2HCl(aq) + Na₂CO₃(s)→2NaCl(aq) + CO₂(g) + H₂O(Z)

10. Reaction of Acids with metal Hydrogen Carbonates:

Acid + Metal Hydrogen Carbonate→ Salt + CO₂ + H₂O

HCl(aq) + NaHCOg(s) NaCl (aq) + CO₂(aq) + H₂O(l)

11. Neutralization reaction:

When the effect of a base is nullified by an acid and vice-versa is called a neutralization reaction.

Base + acid→ Salt + water

NaOH + HCl→ NaCl + H₂O

12. Antacids:

Antacids are mild alkalies and contain sodium hydrogen carbonate. These are used for getting relief from acidity and indigestion and sometimes, even headaches.

13. Reaction of Acids with metallic Oxides:

Acid + Metal Oxides → Salt + Water

2HCl(aq) + CuO(s)

CuCl₂(aq) + H₂O(l)

14. All acids generate H⁺ ions and all bases generate OH^– ions in the presence of water and this helps acids and bases to conduct electricity.

15. Universal indicators:

An indicator which passes through a series of colour changes over a wide range of H₃O⁺ (hydronium) ion concentrations is called a universal indicator. It is a mixture of several indicators.

16. pH: pH is a number which indicates the acidic or basic nature of a solution.

17. pH scale: pH scale is the scale for measuring hydrogen ion or hydronium ion concentration in a solution.

pH =- log [H₃O⁺]

18. Acid rain: When the pH ofrain water is less than 5-6, is called acid rain.

19. Dilute acid: A dilute acid solution containing only a small amount of acid and a large amount of water.

20. Concentrated acid: A concentrated acid contains a large amount of acid and a small amount of water.

21. Salts: Salts are formed by the combination of acids and bases

Examples of Salts:

Sodium chloride: NaCl

Sodium carbonate: Na₂CO₃

Sodium hydrogen carbonate: NaHCO₃

Ammonium nitrate: NH₄NO₃

Potassium sulphate: NH₄NO₃

22. Properties of a Salt Solution:

1. Tastes salty.
2. The colour of the litmus solution usually does not change when added to a salt solution. However, some salts turn blue litmus red whereas others turn red litmus blue.
3. Conducts electricity.

23. Alkali: The hydroxide of metals which dissolve in water are known as alkalies.

24. Normal salt: It does not hydrolyse in water.

25. Acidic salt: It hydrolyses in water to give strong acids like H₂SO₄.

26. Basic salt: It hydrolyses in water to give a strong base like NaOH.

27. Water of crystallization: Water of crystallization is the fixed number of water molecules present in one formula unit of salt.

For example: CuSO₄.5H₂O, Na₂CO₃.10H₂O.

28. Deliquescence: A substance that absorbs moisture gradually from the air is called a deliquescent substance and this phenomenon is called deliquescence.

29. Carbonation: It is a process in which brine (NaCl) saturated with ammonia is allowed to come in contact with carbon dioxide under pressure to form sodium bicarbonate.

30. Antichlor: Antichlor is a substance used to remove excess chlorine from material or cloth.

For example sodium bisulphite, and sodium thiosulphate.

31. Hydrolysis: The interaction of a salt with water to give an acid and base is called salt hydrolysis.

32. Hydrated salts: Some salts crystallize with a fixed number ofwater molecules attached to one formula unit of salt.

33. Common Salt- Sodium Chloride (NaCl)

NaOH + HCl→ NaCl + H₂O

34. Caustic soda- Sodium hydroxide (NaOH)

2 NaCl(aq) +2H₂O(l) → Electricity  → 2NaOH (aq) +Cl(g)+H(g)

35. Bleaching Powder- Calcium Oxychloride (CaOCl₂)

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

36. Baking Soda- Sodium hydrogen Carbonate (NaHCO₃)

NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ + NH₄Cl

37. Washing Soda- Sodium Carbonate decahydrate  → Na₂CO₃.10H₂O

38. Plaster of Paris: CaSO₄. H₂O is known as Plaster of Paris when wetted with water sets to a hard porous mass within 10-15 minutes

CBSE Class 10 Science Chapter 2 Acids And Bases And Salts Short Question And Answers

Question 1. Five solutions A, B, C, D and E when tested with a universal indicator showed pH of 4, 1,11,7 and 9, respectively. Which solution is it?

1. Neutral
2. Strongly alkaline
3. Strongly acidic?
4. Weakly alkaline?

Arrange the pH in increasing order of hydrogen-ion concentration.
Answer:

1. D
2. C
3. B
4. A
5. E

11<9<7<4<1

Question 2. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH₃COOH) is added to test tube B. The amount and concentration taken for both acids are the same. In which test tube will the fizzing occur more vigorously and why?
Answer:

Fizzing will occur more vigorously in test tube A containing hydrochloric acid. This is because hydrochloric acid is stronger than acetic acid and gives more H⁺ ions quickly.

Thus, the reaction between magnesium ribbon and HCl is faster than between Mg and acetic acid.

Question 3. A milkman adds a very small amount of baking soda to fresh milk.

1. Why does he shift the pH ofthe fresh milk from 6 to slightly alkaline?
2. Why does this milk take a long time to set as curd?

Answer:

1. The milkman adds a little baking soda to fresh milk to make it slightly alkaline so that it can be preserved for a longer time.
2. Initially, lactic acid formed is used up to neutralize the base and when more lactic acid is formed, the milk sets as curd.

Question 4. Give two important uses of washing soda and baking soda.
Answer:

Uses of baking soda:

1. It is used in bakery.
2. It is used in soda acid fire extinguishers.

Uses of washing soda:

1. It is used in the manufacture of glass, soap and paper.
2. It is used for removing the permanent hardness of water

Question 5. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents ofeach test tube?
Answer:

1. Dip red litmus paper separately in three test tubes.
2. The test tube in which red litmus turns blue contains the basic solution. Now dip the blue litmus in the other two test tubes.
3. The tube which turns blue litmus red contains the acid solution. The tube in which litmus paper gives a purple colour contains distilled water.

Question 6. Why should curd and sour substances not be kept in brass and copper vessels?
Answer:

1. Curd and sour substances contain acids which react with brass and copper vessels.
2. Thus, brass and copper vessels get corroded.
3. Further, the products formed make the food unfit for eating.

Question 7. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride
Answer:

Since the end product is calcium chloride and the gas formed extinguishes a burning candle, it is CO₂ and metal compound A must be calcium carbonate. Hence, the balanced chemical equation for the reaction is as below

CaCO₃+ 2HCl→CaCl + CO₂ + H₂O

Question 8. Why do HCl, HNO₃, etc., show acidic characteristics in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic characteristics?
Answer:

Compounds like HCl, HNO₃, etc. release H⁺ ions in aqueous solution and hence show acidic character while alcohol and glucose do not release H⁺ ions in aqueous solution, and hence do not show acidic character.

Question 9. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Answer:

When water is added to acid, there is a sudden rise in temperature with explosion and the acid being present in bulk, it gets spilt on your body and clothes.

When an acid is added to water, the water is in bulk and the acid being heavier settles down and the heat evolved is dissipated in the water itself hence, the spurting of the liquid is minimised. For this reason, it is recommended that acid should be added to water in small amounts with stirring to dilute the concentrated acid.

Question 10. What will happen if a solution ofsodium hydrocarbonate is heated1? Give the equation of the reaction involved.
Answer:

Sodium hydrogen carbonate solution on heating gives sodium carbonate, water with evolution of carbon dioxide gas.

2 NaHCO₃(aq) → (Heat) → Na₃CO₂(s)+H₂O(l)+CO₂(g)

Question 11. Write an equation to show the reaction between Plaster of Paris and water.
Answer:

The reaction between Plaster of Paris and water:

⇒ \(\underset{\text { Plaster of Paris }}{2 \mathrm{CaSO}_4 \cdot \frac{1}{2} \mathrm{H}_2 \mathrm{O}}+\mathrm{H}_2 \mathrm{O} \longrightarrow \underset{\text { Gypsum }}{2 \mathrm{CaSO}_4 \cdot 2 \mathrm{H}_2 \mathrm{O}}\)

Question 12. Crystals of copper sulphate are heated in a test tube for some time

1. What is the colour of copper sulphate crystals

1. Before heating, and
2. After heating?

2. What is the source of liquid droplets? Seen on the inner upper side of the test tube during the heating process?

Answer:

1. 

1. Blue
2. White

2. Crystals of copper sulphate (CuSO₄.5H₂O) contain water of crystallisation and on heating these crystals lose water and become white. This lost water can be seen in the form of droplets on the inner upper side ofthe test tube.

Question 13. Effervescence arc formed when the batter for cake is heated. Which substance is present in the batter? Name the gas evolved. Write the chemical equation involved.
Answer:

The substance present is baking soda (NaHCO₃).

The gas evolved in CO

2NaHCO₃ → (Heat)→ Na₂CO₃ + H₂O + CO

Question 14. State the number of water molecules present in crystals of washing soda and Plaster of Paris. What are these water molecules called?
Answer:

1. Washing soda: 10 molecules of water.

Plaster of Paris: 1/2 molecule of water.

2. These molecules are called water of crystallisation.

Question 15. Acids do not show acidic behaviour in the absence of water but do so in water. Justify this statement with the help ofa chemical equation.
Answer:

Acids ionise in aqueous medium to form hydrogen ions. These hydrogen ions cannot exist alone, they exist after combining with water molecules. Thus, aqueous hydrogenions which are responsible for acidic behaviour can exist in the presence of water only.

H⁺(Hydrogen ion)+H₂O(water) + H₃O⁺ (Hydronium ion)

These hydrogen ions are as shown as H⁺(aq) or hydronium ions (H₂O⁺).

Question 16. Give three practical applications of a neutralisation reaction.
Answer:

• Antacids have been developed based on neutralisation reactions.
• Toothpaste is basic which neutralises the excess of acid produced in our mouth.
• Milkman adds a very small amount of baking soda to milk to neutralise the lactic acid produced in the milk.

Question 17.

1. Define olfactory indicators. Name two substances which can be used as olfactory indicators.
2. Choose strong acids from the following:
3. CH₃COOH, H₂SO₄, H₂CO₃, HNO₃

Answer:

1. Those substances whose smell (odour) changes in acidic or basic solution are called olfactory indicators,

Example: Onion and vanilla.

2. H₂SO₄ and HNO₃ are strong acids.

Question 18. 15 mL of water and 10 mL of sulphuric acid are to be mixed in a beaker.

1. State the method that should be followed with reason.
2. What is this process called?

Answer:

1. The acid is to be added slowly in water to prevent the mixture to be splashed. The reaction is highly exothermic, therefore, constant cooling should be done.
2. The process is called dilution.

Question 19. The marble statues are often slowly corroded when kept in open for a long time. Give a suitable reason.
Answer:

Chemically, marble is calcium carbonate. All metal carbonates and hydrogen carbonates react with acids to give corresponding salt, carbon dioxide and water.

Calcium carbonate reacts with acids to form calcium hydrogen carbonate, which is soluble in water and thus washed away. So the marble statues are slowly corroded.

CaCO₃(s) + H₂O(l) + CO₂(g) → Ca(HCO₃)₂(aq)

Question 20.

1. State the purpose of developing scale.
2. Mention the pH range for acids.
3. What is the pH of acid rain and how it affects aquatic life?

Answer:

1. The purpose of developing a pH scale was to quantify the amount of H⁺ or OH^– ions in a solution.
2. The pH range for acids is 0 -7.
3. When the pH ofrain water is less than 5.6, it is called acid rain. It lowers the pH of river water. Thus, the survival of aquatic life becomes difficult.

Question 21. Deepika prepares HCl gas in her school laboratory using certain chemicals. She puts both dry and wet blue litmus papers in contact with the gas.

1. Name the reagents used by Deepika to prepare HCl gas.
2. State the colour changes observed with the dry and wet blue litmus paper.
3. Show the formation of ions when HCl gas combines with water.

Answer:

The reagents used by Deepika to prepare HCl gas are sodium chloride and sulphuric acid.

There is no colour change observed with dry litmus paper. However, wet blue litmus paper turns red.

HCI + H₂O → H₃O⁺ + Cl^–

Question 22.

1. If we take hydrochloric acid and acetic acid of the same concentration, which one will produce less H⁺ ion concentration? Out of two, which one is a weak acid?
2. If someone is suffering from acidity, which ofthe following would you suggest to cure it: Vinegar, orange juice, or baking soda solution? Give reasons for your cone.

Answer:

1.

1. Out of hydrochloric acid and acetic acid of the same concentration, acetic acid will produce fewer H⁺ ions.
2. Acetic acid is weaker than hydrochloric acid.

2. If someone is suffering from acidity,I would suggest baking soda solution to cure it because it neutralises the excess acid produced in the stomach and provides relief.

Question 23. Write the chemical name and formula of the following:

1. Salt is formed by the combination of weak acids like carbonic acid and strong bases like sodium hydroxide.
2. Basic substance formed by the chlor-alkali process.
3. Substances are added in cakes to make them fluffy.

Answer:

1. Sodium carbonate (Na₂CO₃).
2. Sodium hydroxide (NaOH).
3. Sodium hydrogen carbonate (NaHCO₃).

Question 24.

1. Name the products obtained in the chlor-alkali process.
2. Name the gases liberated at the anode and at the cathode respectively.
3. Name the solution which is used as raw material in this process.

Answer:

1. Chlorine gas, hydrogen gas and sodium hydroxide solution.
2. Chlorine gas is given off at the anode and hydrogen gas at the cathode.
3. Brine solution

Question 25. Explain why

1. The colour of copper sulphate crystals changes on heating.
2. Baking soda acts as an antacid.
3. An acid should be added to water while diluting. 

Answer:

1. It loses its 5 molecules of water of crystallisation, hence colour changes.
2. It is alkaline and neutralises excess acid to relieve pain.
3. As dilution of acids is an exothermic reaction and adding water to acids will splash and cause burns

Question 26.

1. Give the chemical names of acids present in

1. Ant
2. Lemon
3. Milk
4. Tomato

2. Write the chemical names of two salts belonging to the sodium family

Answer:

1.

1. Formic acid/methanoic acid
2. Citric acid
3. Lactic acid
4. Oxalic acid

2.

1. Soddiumcarbonate (Na₂CO₃)
2. Sodium sulphate (Na₂SO₄)

Question 27.

1. What do you understand by the term hydrated salt?
2. Give two examples of hydrated salt which are white and state their chemical formula.

Answer:

1. The salts having water of crystallisation with them are known as hydrated salts. Some salts unite with a definite quantity of water while crystallising out from their solutions, and this is known as the water of crystallisation.

2.

1. Sodium sulphate decahydrate (Na₂CO₃.10H₂O). It is commonly known as washing soda.
2. Hydrated calcium sulphate (CaSO₄.2H₂O). It is commonly known as gypsum.

Question 28. Given below are the pH values of our different liquids: 7.0, 14.0, 4.0, 2.0, Which of these could be that of

1. Lemon juice
2. Distilled water
3. 1 M sodium hydroxide solution
4. Tomato juice

Answer:

1. Lemon juice pH = 2.0

2. Distilled water pH = 7.0

3. 1 M NaOH pH = 14.0

4. Tomato juice pH = 4.0

Question 29.

1. Write the name given to bases that are highly soluble in water. Give an example.
2. How is tooth decay related to pH? How can it be prevented?
3. Why does a bee sting cause pain and irritation? Rubbing baking soda on the sting area gives relief. How?

Answer:

1. Alkali Example: NaOH (Sodium hydroxide)
2. The lower the pH, the more will be tooth decay. Acid reacts with Ca3(P04)2 and causes tooth decay. It can be prevented by brushing our teeth after every meal.
3. It is due to formic acid. Sodium hydrogen carbonate (Baking soda) neutralises formic acid giving relief.

Question 30. “Sodium hydrogen carbonate is a basic salt”. Justify the statement. How is it converted into washing soda? Explain.
Answer:

Sodium hydrogen carbonate is a salt of sodium hydroxide (strong base) and carbonic acid (weak acid).

It is a basic salt. It is converted into washing soda by heating followed by crystallisation

2 NaHCO₃ →  (Heat) → Na₂CO₃ + CO₂ +H₂O

Question 31. A white powder is added while baking bread and cakes to make them soft and fluffy. Write the name of the powder. Name its main ingredients. Explain the function ofeach ingredient. Write the chemical reaction taking place when the powder is heated during baking.
Answer:

Baking powder.

It consists of sodium hydrogen carbonate and tartaric acid. Sodium hydrogen carbonate gives CO₂ which makes cake soft and fluffy. Tartaric acid neutralises the bitterness due to the sodium carbonate produced.

2NaHCO₃(s)→  (Heat) → Na₂CO₃(s) +CO₂(g) +H₂O(l)

Question 32. Classify the following salts into acidic, basic and neutral: Potassium, sulphate, ammonium chloride, sodium carbonate, sodium chloride.
Answer:

Neutral: Potassium sulphate, Sodium chloride

Acidic: Ammonium chloride

Basic: Sodium carbonate

Question 33.

1. Name the compound which is obtained from baking soda and is used to
   permanent hardness of water.
2. Write its chemical formula.
3. What happens when it is recrystallised from its aqueous solution?

Answer:

1. Sodium carbonate is obtained from baking soda and is used to remove the hardness of water.
2. Na₂CO₃.
3. It changes to washing soda, Na₂CO₃.10H₂O

Question 34. Tooth enamel is one ofthe hardest substances in our body. How does it undergo damage due to eating chocolates and sweets? How does toothpaste prevent this damage?
Answer:

Tooth enamel is made up of calcium phosphate. Chocolates and sweets produce acid in our mouth which reacts with enamel (calcium phosphate) and leads to cavities. We should brush our teeth after every meal as well as after eating sweets, etc.

Question 35.

1. What is a universal indicator?
2. Write the chemical equation involved in the preparation ofsodium hydroxide. Name the process.

Answer:

1. Universal is a mixture of synthetic Indicators which is used to find pH of solutions,

2. 2NaCl(aq) + 2H₂O(Z)→  (Electrolysis)→ 2NaOH(aq)+ H₂(g) + Cl₂(g)

It is called the chlor-alkali process.

Question 36. What happens when chlorine is passed over slaked lime at 313K? Write the chemical equation of the reaction involved and state two uses ofthe product obtained.
Answer:

Bleaching powder is formed

Ca(OH)₂(s) +Cl₂(g) → (313 K) → CaOCl₂(s)+H₂O(l)

Bleaching powder Uses:

1. It is used as a bleaching agent in paper and textile industries.
2. It is used as a disinfectant in the purification of drinking water.

Question 37. Name the acid present in an ant sting andgive its chemical formula. Also, give a common method to get relief from the discomfort caused by the ant sting.
Answer:

The acid present in ant sting is methanoic acid (formic acid). The chemical formula is HCOOH. To get relief one should apply any available basic salt

Example: Baking soda (NaHCO₃) on it.

Question 38. What happens when nitric acid is added to the shell?
Answer:

Eggshell contains CaCO₃. When nitric acid is added to it, the following reaction takes place with the evolution of CO₂

CaCO₃ + 2 HNO₃ → Ca(NO₃)₂ + H₂O + CO₂

As a result, the shell slowly dissolves in nitric acid.

Question 39. A student prepared solutions of

1. An acid and
2. A base in two separate beakers.

She forgot to label the solutions and litmus paper is not available in the laboratory. Since both the solutions are colourless, how will she distinguish between the two?
Answer:

If litmus paper is not available, phenolphthalein and methyl orange can be used.

Take a few drops of the two solutions in two separate test tubes. Add 1-2 drops of phenolphthalein in each of them. The solution which turns phenolphthalein pink is a base.

The other solution (acidic) will remain colourless. Clean the test tubes and repeat the experiment with methyl orange. The solution which turns methyl orange red is an acid. The colour in the other (basic) solution will be yellow.

Question 40. Salt A commonly used in bakery products on heating gets converted into another salt B which itself is used for the removal of the hardness of water and a gas C is evolved. The gas C when passed through lime water, turns it milky. Identify A, B, and C. Heat
Answer:

So A = NaHCO₃

B = Na₂CO₃

C = CO₂

Question 41. What are strong and weak acids? In the following list of acids, separate strong acids from weak acids. Hydrochloric acid, citric acid, acetic acid, nitric acid, formic acid, sulphuric acid.
Answer:

In aqueous solutions, strong acids ionise completely and provide hydronium ions. On the other hand, weak acids are partially ionised and an aqueous solution of the same molar concentration provides a much smaller concentration of H₃O⁺ ions.

1. Strong acids—Hydrochloric acid, sulphuric acid, nitric acid
2. Weak acids—Citric acid, acetic acid, formic acid

Question 42. When zinc metal is treated with a dilute solution ofa strong acid, a gas is evolved, which is utilisedin the hydrogenation of oil. Name the gas evolved. Write the chemical equation ofthe reaction involved and also write a test to detect the gas formed.
Answer:

When zinc reacts with a dilute solution of strong acid, it forms salt and hydrogen gas is evolved.

Zn + 2HCl→  ZnCl₂ + H₂

When a burning splinter is brought near the mouth ofthe test tube, the gas burns with a pop sound.

Question 43. Kiran was suffering from toothache. She never brushed her teeth before sleeping at night.

1. She loves to eat chocolates and ice cream.
2. What is, in general, the cause of toothache?
3. What our teeth are made up of?
4. How does toothpaste help in preventing toothache?

Answer:

1. Tooth decay starts when pH of the mouth is lower than 5.5. The acid so produced attacks the teeth and produces cavities which cause pain.
2. Calcium phosphate.
3. Toothpaste is generally basic, thus it helps in neutralising acids.

Question 44. Karan’s mother had severe pain when a honeybee stung her hand. Karan’s granny tried to relieve the pain by rubbing a metal on the stung area. But Karan picked up the baking powder from the kitchen and applied it on her mother’s hand which quickly relieved the pain.

1. Why does honeybee stinging cause pain?
2. How does baking powder relieve the bee-sting pain?
3. What value of Karan is seen in the above case?

Answer:

1. Honeybee sting consists of acid that is released in our body and causes pain.
2. Baking powder is basic, it neutralises the acid released in our body by bee-sting and relieves the pain.
3. Karan showed the value of prompt, proactive and responsible behaviour.

Question 45. Pooja’s friend is very fond, of coffee. He drinks a cup of coffee every day before he goes to school and faces the problem of stomachache very often. Pooja advised him not to drink coffee in the morning.

1. What was the cause of stomachache?
2. What would be the pH of stomach juices after consuming coffee?
3. What values of Pooja are reflected in the above act?

Answer:

1. A cup of coffee causes acidity that leads to stomachache.
2. The pH of the stomach after drinking coffee is 5.
3. Pooja showed the value of concern, caring and awareness.

Question 46. Substance A, an oxide of group 2 elements, is used intensively in the cement industry. This element is present in bones also. On treatment with water, it forms a solution which turns red litmus blue. Identify A’ and also write the chemical reaction involved.
Answer:

A is calcium and chemical reaction involved:

CaO(s) + H₂O(Z) → (Basic solution)Ca(OH)₂(aq)

Question 47. What happens when the shell is placed in concentrated nitric acid in a beaker?
Answer:

Evolution of CO₂ occurs and the shell dissolves slowly

⇒ \(\mathrm{CaCO}_3+2 \mathrm{HNO}_3(\text { Conc. }) \longrightarrow \mathrm{Ca}\left(\mathrm{NO}_3\right)_2+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2(\uparrow)\)

Question 48. In one ofthe industrial processes used for the manufacture of NaOH, a gas X’ is formed as a by-product. The gas ‘X reacts with lime water to give a compound which is used as a bleaching agent in the chemical industry. Identify X’ and IT.
Answer:

X = Cl₂ and Y = CaOCl₂

⇒ \(\mathrm{Ca}(\mathrm{OH})_2+\underset{[\mathrm{X}]}{\mathrm{Cl}_2} \longrightarrow \underset{[\mathrm{Y}]}{\mathrm{CaOCl}_2}+\mathrm{H}_2 \mathrm{O}\)

CBSE Class 10 Science Chapter 2 Acids And Bases And Salts Multiple Choice Questions

Question 1. What happens when a solution of an acid is mixed with a tube?

1. The temperature ofthe solution increases

2. The temperature ofthe. solution decreases

3. The temperature ofthe solution remains the

4. Salt formation takes place

1. 1only
2. 1 and 3
3. 2 and 3
4. 1 and 4

Answer: 4.1 and 4

Question 2. An aqueous solution turns red litmus solution blue. Excess addition of which of the following solutions would reverse the change? solution of a base in a test same

1. Baking powder
2. Lime
3. Ammonium hydroxide solution
4. Hydrochloric acid

Answer: 4. Hydrochloric acid

Question 3. During the preparation of hydrogen chloride gas on a humid day, the gas is usually passed through the guard tube containing calcium chloride. The role of calcium chloride taken in the guard tube is to

1. Absorb the evolved gas
2. Moisten the gas
3. Absorb moisture from the gas
4. Absorb Cl^– ions from the evolved gas

Answer: 3.  Absorb moisture from the gas

Question 4. Which ofthe following salts does not contain water of crystallisation?

1. Blue vitriol
2. Baking soda
3. Washing soda
4. Gypsum

Answer:  2. Baking soda

Question 5. Sodium carbonate is a basic salt because it is a salt of

1. Strong acid and strong base
2. Weak acid and weak base
3. Strong acid and weak base
4. Weak acid and strong base

Answer: 4. Weak acid and strong base

Question 6. Calcium phosphate is present in tooth enamel. Its nature is

1. Basic
2. Acidic
3. Neutral
4. Amphoteric

Answer: 1.  Basic

Question 7. A sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the pH paper yellowish-orange. Which of the following would change the colour of the paper to greenish-blue?

1. Lemon juice
2. Vinegar
3. Common salt
4. An antacid

Answer: 4. An antacid

Question 8. Which of the following gives the correct increasing order of acidic strength?

1. Water < Acetic acid < Hydrochloric acid
2. Water < Hydrochloric acid < Acetic acid
3. Acetic acid < Water < Hydrochloric acid
4. Hydrochloric acid < Water < Acetic acid

Answer: 1.  Water < Acetic acid < Hydrochloric acid

Question 9. If should a few be dropped of? a concentrated acid accidentally spills over the hand ofa student, what should be done?

1. Wash the hand with saline solution
2. Wash the hand immediately with plenty of water and apply a paste ofsodium hydrogen carbonate
3. After washing with plenty of water, apply a solution of sodium hydroxide to the hand
4. Neutralise the acid with a strong alkali

Answer: 2.  Wash your hand immediately with plenty of water and apply a paste ofsodium hydrogen carbonate

Question 10. Sodium hydrogen carbonate when added to acetic acid evolves a gas. Which of the following statements are true about the gas evolved?

1. It turns lime water milky

2. It extinguishes a burning splinter

3. It dissolves in a solution ofsodium hydroxide

4. It has a pungent odour

1. 1 and 2
2. 1, 2 and 3
3. 2, 3 and 4
4. 1 and 4

2.  1, 2 and 3

Question 11. Common salt besides being used in the kitchen can also be used as the raw material for making

1. Washing soda

2. Bleaching powder

3. Baking soda

4. Slaked lime

1. 1 and 3
2. 2 and 3
3. 1 and 4
4. 2 and 4

Answer: 3.  1 and 4

Question 12. One of the constituents of baking powder is sodium hydrogen carbonate, the other constituent is

1. Hydrochloric acid
2. Tartaric acid
3. A cetic acid
4. Sulphuric acid

Answer:  2. Tartaric acid

Question 13. To protect from tooth decay we are advised to brush our teeth regularly. The nature of the toothpaste commonly used is

1. Acidic
2. Neutral
3. Basic
4. Corrosive

Answer: 3. Basic

Question 14. Which ofthe following statements is correct about an aqueous solution of an acid and of a base?

1. The higher the pH, the stronger the acid

2. The higher the pH, the weaker the acid

3. The lower the pH, the stronger the base

4. The lower the pH, the weaker the base

1. 1 and 3
2. 2 and 3
3. 1 and 4
4. 2 and 4

Answer: 4. 2 and 4

Question 15. The pH of the gastric juices released during digestion is

1. Less than 7
2. More than 7
3. Equal to 7
4. Equal to 0

Answer: 1. Less than 7

Question 16. Which ofthe following phenomena occur, when a small amount of acid is added to water?

1. Ionisation

2. Neutralisation

3. Dilution

4. Salt formation

1. 1 and 2
2. 1 and 3
3. 2 and 3
4. 2 and 4

Answer:  2. 1 and 3

Question 17. Which one ofthe following can be used as an acid-base indicator by a visually impaired student?

1. Litmus
2. Turmeric
3. Vanilla essence
4. PetuniaI leaves

Answer: 3. Vanilla essence

Question 18. Which of the following substances will not give carbon dioxide on treatment with dilute acid?

1. Marble
2. Limestone
3. Baking soda
4. Lime

Answer: 4. Lime

Question 19. Which ofthe following is acidic?

1. Lime juice
2. Human blood
3. Lime water
4. Antacid

Answer: 1.  Lime juice

Question 20. In an attempt to demonstrate electrical conductivity through an electrolyte, the following apparatus was set up.

1. Which among the following statement(s) is(are) correct?

2. The bulb will not glow because the electrolyte is not acidic

3. The bulb will glow because NaOH is a strong base and furnishes ions for conduction

4. The bulb will not glow because the circuit is incomplete

The bulb will not glow because it depends upon the type of electrolytic solution

1. 1 and 3
2. 2 and 4
3. 2 only
4. 4 only

Answer: 3. 2 only

Question 21. Which ofthe following is used for the dissolution of gold?

1. Hydrochloric acid
2. Sulphuric acid
3. Nitric acid
4. Aqua regia

Answer: 4.  Aqua regia

Question 22. Which of the following is not a mineral acid?

1. Hydrochloric acid
2. Citic acid
3. Sulphuric acid
4. Nitric acid

Answer: 2. Citic acid

Question 23. Which among the following is not a base?

1. NaOH
2. KOH
3. NH₄OH
4. C₂H₅OH

Answer: 4.  C₂H₅OH

Question 24. Which ofthe following statements is not correct?

1. All metal carbonates react with acid to give a salt, water and carbon
   dioxide
2. All metal oxides react with water to give salt and acid
3. Some metals react with acids to give salt and hydrogen
4. Some non-metal oxides react with water to form an acid

Answer: 2.  All metal oxides react with water to give salt and acid

Question 25. Match the chemical substances given in Column (A) with their appropriate application given in Column (B)

1. 1-B,2-A,3-D,4-C
2. 1-C,2-B,3-D,4-A
3. 1-C,2-D,3-1,4-2
4. 1-B,2-D,3-A,4-C

Answer: 3.  1-C,2-D,3-1,4-2

Question 26. Equal volumes of hydrochloric acid and sodium hydroxide solutions of the same concentration are mixed and the pH of the resulting solution is checked with pH paper. What would be the colour obtained? (You may use the colour guide given below.)

1. Red
2. Yellowish-orange
3. Yellowish green
4. Blue

Answer: 3. Yellowish green

Question 27. Which ofthe following is(are) true when HCl(g) is passed through water?

1. It does not ionise in the solution as it is a covalent compound.

2. It ionises in the solution

3. It gives both hydrogen and hydroxyl ions in the solution

4. It forms hydronium ions in the solution due to the combination of hydrogen ions with a water molecule

1. 1 only
2. 3 only
3. 2 and 4
4. 3 and 4

Answer: 3. 2 and 4

Question 28. Which of the following statements is true for acids’?

1. Bitter and change red litmus to blue
2. Sour and change red litmus to blue
3. Sour and change blue litmus to red
4. Bitter and change blue litmus to red

Answer: 3. Sour and change blue litmus to red

Question 29. Which ofthe following are present in a dilute aqueous solution of hydrochloric acid?

1. H₃O⁺+ Cl^–
2. H₃O⁺+ OH^–
3. Cl^– + OH^–
4. Unionised HCl

Answer: 1. H₃O⁺+ Cl^–

Question 30. Identify the correct representation ofreaction occurring during the chlor-alkali process

1. 2NaCl(l) + 2H₂O(l) → 2NaOH(Z) + Cl₂(g) + H₂(g)
2. 2NaCl(aq) + 2H₂O(aq)→  2NaOH(aq) + Cl₂(g) + H₂(g)
3. 2NaCl(aq) + 2H₂O(l) → 2NaOH(ag) + Cl₂(aq) + H₂(aq)
4. 2NaCl(aq) + 2H(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)

Answer: 4.  2NaCl(aq) + 2H₂O(l) → 2NaOH(ag) + Cl₂(aq) + H₂(aq)

Question 31. Match the given in Column (A) with the correct source given in Column (B)

Answer: 1-D ,2-C ,3- B ,4-A

Question 32. Match the important chemicals given in Column (A) with the chemical formulae given in Column (B)

Answer: 1- B, 2-C, 3- D,4- A

Question 33. A solution turns red litmus blue. ItspH is likely to be

1. 1
2. 4
3. 5
4. 10

Answer: 4. 10

Question 34. A solution reacts with crushed eggshells to give a gas that turns lime-water milky. The solution contains

1. NaCl
2. HCl
3. LiCl
4. KCl

Answer: 4. KCl

Question 35. 10 mL ofa solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralise it will be

1. 4 mL
2. 8 mL
3. 12 mL
4. 16 mL

Answer: 4. 16 mL

Question 36. Which one ofthe following types of medicines is used for treating indigestion?

1. Antibiotic
2. Analgesic
3. Antacid
4. Antiseptic

Answer: 3. Antacid

CBSE Class 10 Science Class 10 Science Chapter 1 Chemical Reactions And Equations

Representation of Chemical Reaction

CBSE Class 10 Science Class 10 Science Chapter 1 Chemical Reactions And Equations Definitions

1. Chemical reaction: Whenever a chemical change occurs, we can say that a chemical reaction occurs.

2. The following observations help us determine whether a chemical reaction occurred.

1. Change in state
2. Change in colour
3. Evolution of a gas
4. Change in temperature

3. Chemical equation: A chemical change can be represented symbolically in terms of a chemical equation.

Read and Learn More CBSE Class 10 Science Short Answer Questions

4. A chemical equation represents a chemical reaction occurring in a chemical change.

5. To make a chemical reaction more informative, the physical states of the reactants and products are mentioned along with their chemical formulae. The gaseous, liquid, aqueous and solid states of reactants and products are represented by notations (g), (l), (aq) and (s) respectively.

6. Mass can neither be created nor destroyed in a chemical reaction, that is, the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants.

7. Balancing equation: A chemical reaction is balanced so that the number of atoms to each element involved in a chemical reaction is the same on the reactant and product sides.

8. Combination reaction: The reaction in which two or more substances combine to form a new single substance.

For example:

⇒ \(\underset{\text { Calcium oxide(Quicklime) }}{\mathrm{CaO}(s)}+\underset{\text { Water }}{\mathrm{H}_2 \mathrm{O}(l)} \longrightarrow \underset{\text { Calcium hydroxide(Slaked lime) }}{\mathrm{Ca}(\mathrm{OH})_2(a q)}\)

9. Decomposition reaction:

The reaction in which a single substance decomposes to give two or more substances. It can be thermal (by heat) electrolytic (by electric current) decomposition or photochemical (by sunlight). For example,

2 Pb (NO)₂(s) (Lead nitrate) →  (heat) → 2 PbO(s)(Lead oxide)  + 4 NO₂ (g) +O₂(g)

10. Displacement reaction:

The chemical reaction in which an element displaces another element from its compound.

For example:

⇒ \(\underset{\text { Iron }}{\mathrm{Fe}(s)}+\underset{\text { Copper sulphate }}{\mathrm{CuSO}_4(a q)} \longrightarrow \underset{\text { Iron sulphate }}{\mathrm{FeSO}_4(a q)}+\underset{\text { Copper }}{\mathrm{Cu}(s)}\)

11. Double displacement reaction:

The reaction is in which two different atoms or groups of atoms (ions) are mutually exchanged.

For example:

⇒ \(\underset{\text { Sodium sulphate }}{\mathrm{Na}_2 \mathrm{SO}_4(a q)}+\underset{\text { Barium chloride }}{\mathrm{BaCl}_2(a q)} \rightarrow \underset{\text { Barium sulphate }}{\mathrm{BaSO}_4(s)}+\underset{\text { Sodium chloride }}{2 \mathrm{NaCl}(a q)}\)

12. Precipitation reaction: The reaction that produces precipitation (insoluble salt) is called precipitation reaction.

For example:

⇒ \(\underset{\text { Silver nitrate }}{\mathrm{AgNO}_3(a q)}+\underset{\text { Sodium chloride }}{\mathrm{NaCl}(a q)} \longrightarrow \underset{\begin{array}{c}
\text { Silver chloride } \\
\text { (white pott }
\end{array}}{\mathrm{AgCl}(s)}+\underset{\text { Sodium nitrate }}{\mathrm{NaNO}_3(a q)}\)

13. Neutralisation reaction: When acids react with bases or alkalis their acidity is destroyed and a salt is produced; such reactions are known as neutralisation reactions.

For example:

⇒  \(\underset{\begin{array}{c}
\text { Hydrochloric } \\
\text { acid }
\end{array}}{\mathrm{HCl}}+\underset{\text { Sodium hydroxide }}{\mathrm{NaOH}} \longrightarrow \underset{\text { Sodium chloride }}{\mathrm{NaCl}}+\underset{\text { Water }}{\mathrm{H}_2 \mathrm{O}}\)

14. Isomerisation reaction:

Those reactions in which the atoms present in the molecules of the reactant are rearranged are known as isomerisation reactions.

For example:

NH₄CNO(Ammoniumcyanate) →(heat) → H₄N-CO-NH₄(urea)

15. Photochemical reaction: The reaction which takes place in the presence of light is called photochemical reaction.

For example:

2AgBr(s) (silver bromide) → (sunlight) → 2 Ag(Silver) +Br₂ (Bromine)

16. Exothermic reaction: The reaction in which heat is given out along with the products.

⇒ \(\underset{\text { Carbon }}{\mathrm{C}(\mathrm{s})}+\underset{\text { Oxygen }}{\mathrm{O}_2(\mathrm{~g})} \longrightarrow \underset{\text { Carbon dioxide }}{\mathrm{CO}_2(\mathrm{~g})}+\text { Heat }\)

17. Endothermic reaction: The reaction in which energy is absorbed by the reactants.

N₂(g)(Nitrogen) +O₂(g)(oxygen) → (heat) →  2NO(g) (Nitric oxide)

18. Oxidation: It is the gain of oxygen or the loss of hydrogen.

For example:

2 Cu (Copper) +O₂(Oxygen) → (heat)→ 2CuO(Copper oxide)

19. Reduction: It is the loss of oxygen or gain of hydrogen. For example

CuO(Copper oxide) +H₂ → (heat)→ Cu (Copper)  +HO(water)

20. Redox reaction: The reaction in which one reactant gets oxidised while the other gets reduced.

21. Oxidising agent: The substance which helps in oxidation is called oxidising agent.

22. Reducing agent: The substance which helps in reduction is called reducing agent.

23. Corrosion: When a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion.

For example:

1. The reddish-brown coating on iron
2. The black coating on the silver
3. The green coating on the copper

24. Rancidity: When fats and oils are oxidised, they become rancid and their smell and taste change.

25. Antioxidants: The substances which prevent oxidation are added to foods containing fats and oils

CBSE Class 10 Science Class 10 Science Chapter 1 Chemical Reactions And Equations Short Question And Answers

Question 1. Why should a magnesium ribbon be cleaned before burning in the air?
Answer:

On exposure to air magnesium ribbon gets covered with a layer of magnesium carbonate. So magnesium ribbon should be cleaned with as and paper so that only clean magnesium ribbon is available for burning in air.

Question 2. Write the balanced equation for the following chemical reactions.

1. Hydrogen + Chlorine → Hydrogen chloride
2. Barium chloride + Aluminium sulphate chloride → Barium sulphate + Aluminium
3. Sodium + Water  →  Sodium Hydroxide +Hydrogen

Answer:

1. H₂ + Cl₂ → 2 HCl

2. 3BaCl₂ + Al₂ (SO₄)₃ → 3BaSO₄ + 2AlCl

3. 2Na + 2H₂O→  2NaOH₄+ H₂

Question 3. Write a balanced chemical equation with state symbols for the following reactions.

1. Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
2. Sodium hydroxide solution (in water) reacts with a hydrochloric acid solution (in water) to produce sodium chloride solution and water.

Answer:

1. BaCl₂(aq) (Barium chloride) + Na₂SO₄(aq) (Sodiumsulphate)→ BaSO₄(s)(Barium sulphate)+2 NaCl (aq)(Sodium chloride

2. NaOH(aq) (Sodium hydroxide)+ HCl(sq) (Hydrochloric acid) → NaCl(aq) (Sodium chloride)  + H₂O(Water)

Question 4. A solution ofa substance ‘X? is used for whitewashing.

1. Name the substance ‘X and write its formula.
2. Write the reaction ofthe substance ‘X’ named in (i) above with water.

Answer:

1. X is quick lime and its formula is CaO.

2. CaO(s) (Quick lime) +H₂O(Water) → Ca(OH)₂(aq)(Slakedlime or calcium hydroxide)

Question 5.  Why is the amount of gas collected in one of the test tubes double the amount collected in the other? Name this gas.
Answer:

Water containing a few drops of dilute sulphuric acid is electrolysed using graphite anode and cathode. H₂ gas is collected at the cathode and oxygen at the anode.

The electrochemical reaction is:

2HO(l) → 2H₂(g)+O₂(g)

Thus the amount of hydrogen gas collected is double that of oxygen. If the two gases are collected in two different test tubes, the gas collected in one test tube (i.e., H₂) is double that collected in the other test tube (i.e., oxygen).

Question 6. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Answer:

This is a displacement reaction.

Fe(s)(Iron nail)+ CuSO₄(aq)  → FeSO₄(aq) + Cu(s) (Copper)

Since copper sulphate is blue in colour and iron sulphate is greenish, the colour of copper sulphate changes when an iron nail is dipped in it.

Question 7. Give an example of a double displacement reaction other than the one given in
Answer:

AgNO₃(ag)(Silver nitrate ) + NaCl(aq)(Sodium chloride ) →  AgCl(s)(Silver chloride) + NaNO₃(aq)(Sodium nitrate)

Thus silver exchanges chloride from sodium chloride, and sodium chloride exchanges nitrate ions from silver nitrate. This is a double displacement reaction.

Question 8. Identify the substances that are oxidised and the substances that are reduced in the following reactions.

1. 4Na(s) + O₂(g) →  2Na₂O(s)
2. CuO(s) + H₂(g) →  Cu(s) + H₂O(Z)

Answer:

1. Na(s) is oxidised to Na₂O
2. (s) and oxygen is reduced to O^2- (NaO₂(s)).
3. CuO(s) is reduced to Cu(s) and H₂(g) is oxidised to H₂O(Z).

Question 9. What is a balanced chemical equation? Why should chemical equations be balanced1
Answer:

In a balanced equation the number ofatoms ofeach element on both sides ofthe equation are equal. The chemical equation must be balanced with the aspect of mass because matter can neither be created nor destroyed.

The equation must be balanced concerning charge because the electrons lost by atoms to form cations are equal to electrons gained by other atoms to form anions. Free electrons do not exist in solution.

Question 10. Write the balanced chemical equations for the following reactions:

1. Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
2. Zinc + Silver nitrate → Zinc nitrate + Silver
3. Aluminium + Copper chloride → Aluminium chloride + Copper
4. Barium chloride + Potassium sulphate → Barium, sulphate + Potassium chloride

Answer:

Ca(OH)₂+ CO₂ → CaCO₃ + H₂O

Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag

2Al + 3CuCl → 2AlCl₃ + 3Cu

BaCl₂+ K₂SO₄  → 4 BaSO₄ + 2KCl

Question 11. Why is respiration considered an exothermic reaction? Explain.
Answer:

During digestion, food is broken down into simpler substances. Food like rice, potatoes and bread are made up of carbohydrates. These carbohydrates are further broken down into glucose. Glucose during respiration (inhalation of oxygen) is oxidised with the

Liberation of energy as shown below:

C₆H₁₂ O₆ (Glucose)+ 6O₂(aq)(Oxygen) + 6CO₂(aq)  → 6CO₂  (Carbon dioxide)(aq) + 6H₂O(l) (Water)+ energy

Thus, respiration is an exothermic process.

Question 12. In the refining of silver, the recovery of silver from silver nitrate solution involves displacement by copper metal. Write down the reaction involved.
Answer:

The involved reaction is:

⇒ \(\mathrm{Cu}(s)+2 \mathrm{AgNO}_3(a q) \longrightarrow \mathrm{Cu}\left(\mathrm{NO}_3\right)_2(a q)+2 \mathrm{Ag}(s)\)

Question 13. What do you mean by a precipitation reaction? Explain by giving an example.
Answer:

When two reactants in a solution react and one or more of the products are insoluble or form a precipitate, the reaction is called a precipitation reaction.

For example, when a solution of iron chloride and ammonium hydroxide is mixed, a brown precipitate of iron hydroxide is formed.

FeCl₃(aq)(Ferric chloride) + 3NH₄OH(aq)(Ammoniumhydroxide) → Fe(OH)₃(s) (Ferriuc hydroxide)  +3NH₄Cl(aq) (Ammonium chloride)

Question 14. Why do we apply paint on iron articles?
Answer:

It is observed that iron articles are shiny when new but get coated with a reddish-brown surface when left for some time as the iron articles get rusted. This process is called corrosion. To prevent rusting of iron, paint is applied on iron articles.

Question 15. What happens chemically when quicklime is added to water filled in a bucket?
Answer:

Quicklime reacts with water to form slaked lime and produces a lot of heat and hissing sound

⇒ \(\underset{\begin{array}{c}
\text { Quicklime } \\
\text { (Calcium oxide) }
\end{array}}{\mathrm{CaO}(s)}+\underset{\text { Water }}{\mathrm{H}_2 \mathrm{O}(l)} \longrightarrow \underset{\begin{array}{c}
\text { Slaked lime } \\
\text { (Calcium hydroxide) }
\end{array}}{\mathrm{Ca}(\mathrm{OH})_2(s)}+\text { Heat + Hissing sound }\)

Question 16. Study the reactions given below. State which of the following chemical reactions will take place or not, giving suitable reason for each:

1. Zn(s) + CuSO₄  (aq) → ZnSO₄(aq) + Cu(s)
2. Fe(s) + ZnSO₄(aq)→ FeSO₄(aq) + Zn(s)
3. Zn(s) + FeSO₄(aq) →  ZnSO₄(aq) + Fe(s)

Answer:

1. Zinc is more reactive than copper; so it will displace copper from CuS04. This reaction will take place.
2. Iron is less reactive than zinc, so it cannot displace zinc from zinc sulphate. The reaction will not take place.
3. Zinc is more reactive than iron, it will displace iron from FeS04. The reaction will take place.

Question 17. What is meant by the skeletal-type chemical equation? What does it represent? Using the equation for electrolytic decomposition ofwater, differentiate between a skeletal chemical equation and a balanced chemical equation.
Answer:

The equations in which gaseous are written in atomic form instead of molecular form and the equation is not balanced are called skeletal type chemical equations.

They represent gaseous elements formed in the atomic state and the equation is not balanced

⇒ \(\mathrm{H}_2 \mathrm{O}→ {\text { Electrolysis }} →\mathrm{H}+\mathrm{O} \text { (Sketal equation) }\)

Hydrogen and oxygen are written in atomic forms and the equation is not balanced.

H₂ O → 2H₂ + O₂ (Balanced chemical equation)

H₂ O → H₂ + O₂ is the Skeletal equation.

Question 18. What is redox reaction? When a magnesium ribbon burns in the air with a dazzling flame and forms white ash, is magnesium oxidised or reduced? Why?
Answer:

The reaction in which oxidation (loss ofelectrons) and reduction (gain of electrons) take place simultaneously is called a redox reaction.

⇒ \(\underset{\text { Magnesium }}{2 \mathrm{Mg}(s)}+\underset{\text { Oxygen }}{\mathrm{O}_2(g)} \longrightarrow \underset{\text { Magnesium oxide }}{2 \mathrm{MgO}(s)}\)

Magnesium is getting oxidised because it is losing electrons from Mg²⁺ and oxygen is gaining electrons to form O^2- therefore it is getting reduced.

Question 19. Distinguish between a displacement reaction and a double displacement reaction. Identify the displacement and the double displacement reaction from the following reactions:

1.  HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
2. Fe(s) + CuSO₄(aq) → FeSO₄(aq) +Cu(s)

Answer:

A displacement reaction is a reaction in which more reactive metal can displace less reactive metal from its salt solution.

Double displacement reaction: The reaction is in which a compound exchanges its ions to form two new compounds called double displacement reaction.

1. Double displacement reaction
2. Displacement reaction

Question 20.

1. When a metal ‘X’ is added to the salt solution ofa metal Y following chemical reaction takes place: Metal X + Salt solution of ‘Y’→ Salt solution of ‘X’ + Metal ‘Y’

2. Mention the inference you draw regarding the reactivity of metals ‘X and Y’ and also about the type of reaction. State the reason for your conclusions.
Answer:

It is a displacement reaction.

1. Metal X is more reactive than metal Y.
2. Metal X is displacing metal Y from its salt solution.

A more reactive metal displaces a less reactive one from its salt solution. X is more reactive than Y.

Question 21. Write the essential condition for the following reactions to take place: 2Ag + Cl₂ and write one use of this reaction.
Answer:

1. To carry out the reaction 2AgCl → 2Ag + Cl₂ presence ofsunlight is essential.

This reaction is used in black-and-white photography

Question 22. Name the reducing agent in the following reaction

3MnO₂ + 4Al → 3Mn + 2Al₂O₃

State which is more reactive, Mn or Al and why?

Answer:

‘Al’ is a reducing agent.

‘Al’ is more reactive than Mn.

∴ ‘Al’ displaces Mn from its oxide.

Question 23. Identify the type ofreaction from the following equations.

1. CH₄ + 2O₂ → CO₂ + 2H₂O
2. Pb(NO₃)₂+ 2KI→ Pbl₂+ 2KNO₃
3. CaO + H₂O→ Ca(OH)₂
4. CuSO₄ + Zn→ZnSO₄ + Cu

Answer:

1. Combustion reaction
2. Double displacement reaction
3. Combination reaction
4. Displacement reaction

Question 24. Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer.
Answer:

Any two of these observations will suggest a chemical reaction has taken place

1. Change in state
2. Change in colour
3. Evolution of gas
4. Change in temperature

For example, lead nitrate is a white crystalline solid, on heating it gives a yellowish-brown solid (lead monoxide), brown gas is evolved and a colourless gas is evolved.

It shows chemical reaction has taken place.

Question 25. State what changes in the colour of the iron nail and copper sulphate solution are observed when an iron nail is dipped into copper sulphate solution for about 20 minutes. Write the equation for the reaction that takes place. Also, name the type ofreaction involved in the above process.
Answer:

1. The iron nail becomes brownish and the blue colour of the copper sulphate solution fades.
2. Fe(s) + CuSO₄(aq)→  FeSO₄(aq) + Cu(s)
3. Displacement reaction

Question 26. What is observed when a solution of potassium iodide is added to a solution of lead nitrate? Name the type ofreaction. Write a balanced chemical equation to represent the above chemical reaction.
Answer:

A yellow precipitate of lead iodide is formed. It is a precipitation reaction.

Pb(NO₃)₂ (aq) + 2KI (aq)→Pbl₂ (s) + 2KNO₃ (aq)

It is also called a double displacement reaction.

Question 27. Explain giving chemical equation of any two uses of chemical decomposition reaction in industry.
Answer:

1. In manufacturing cement, quicklime is used and it is obtained by thermal decomposition of limestone.

CaCO₃(s) → (Heat) →CaO(s) + CO₂(g)

2. In manufacturing photochromic glass, silver chloride/bromide is used which turns grey in sunlight.

Question 28. 2 g of lead nitrate powder is taken in a boiling tube. The boiling tube is heated over a flame. Now answer the following:

1. State the colour ofthe fumes evolved and the residue left.
2. Name the type of chemical reaction that has taken place stating its balanced chemical equation.

Answer:

1. Brown-coloured fumes of NO₂ gas are evolved and a yellowish-brown residue is formed.

2. Decomposition reaction has taken as,

2Pb(NO₃)₂(s) → (Heat) → 2PbO(s)+4NO₂(g)+ O₂(g)

Question 29. What is meant by a balanced chemical equation? Why chemical equations are balanced? Balance the chemical equation given below:

Al₂O₃ + NaOH→ NaAlO₂ + H₂O

Answer:

A chemical equation in which the number of atoms of each type involved is the same on the reactants and products is called a balanced chemical equation.

To justify the law of conservation of mass in a reaction, a chemical equation is to be balanced.

Al₂O₃ + 2NaOH→ 2NaAlO₂ + H₂O

Question 30. What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride? State the physical conditions of reactants in which the reaction between them will not take place. Write the balanced chemical equation for the action and name the type ofreaction.
Answer:

A white precipitate of barium sulphate is formed.

If both reactants are in solid state, the reaction will not take place between them.

BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)

It is a double displacement as well as a precipitation reaction.

Question 31. Write balanced chemical equations for the following reactions.

1. Silver bromide on exposure to sunlight decomposes into silver and bromine.
2. Sodium metal reacts with water to form sodium hydroxide and hydrogen gas.

Answer:

1. 2AgBr(s) →  (Sunlight) → 2Ag(s)+Br(g)

2. 2Na(s) + 2H₂O(l)→ 2NaOH(aq) + H₂(g)

Question 32. Give an example each for thermal decomposition and photochemical decomposition reactions. Write relevant balanced chemical equations also.
Answer:

Thermal decomposition reaction

(Copper carbonate -Green)CuCO(s)→ (Heat) → CuO(s)(Copper oxide -Black)+CO₂(g)

Photochemical decomposition reaction

2 AgCl(s) → (Sunlight) → 2 Ag(s)+Cl₂(g)

Question 33.

1. Why is a combustion reaction an oxidation reaction?
2. How will you test whether the gas evolved in a reaction is hydrogen? 

Answer:

1. A combustion reaction is an oxidation reaction because it is always carried in the presence of air or oxygen.

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)

2. Bring a burning matchstick close to the mouth ofthe tube from which hydrogen gas escapes. The gas will immediately catch fire and this will be accompanied by a pop sound.

Question 34. An aluminium can was used to store the ferrous sulphate solution. It is observed that in a few days, holes appeared in the can. Explain the observation and write a chemical equation to support your answer.
Answer:

Aluminium being more reactive displaces ferrous ions from ferrous sulphate solution and this results in the appearance of holes in the aluminium can.

⇒ \(2 \mathrm{Al}(s)+\underset{\text { (Ferrous sulphate) }}{3 \mathrm{FeSO}_4(a q)} \longrightarrow \underset{\text { (Aluminium sulphate) }}{\mathrm{Al}_2\left(\mathrm{SO}_4\right)_3(a q)}+3 \mathrm{Fe}(s)\)

Question 35. Identify the type ofreaction from the following equations:

1. CH₄ + 2O₂-4 →  CO₂ + 2H₂O
2. Pb(NO₃)₂ + 2KI→  Pbl₂ + 2KNO₃
3. CaO + H₂O→ Ca(OH)₂
4. CuSO₄ + Zn→ ZnSO₄ + Cu

Answer:

1. Combustion reaction and oxidation reaction

2. Double displacement and precipitation reaction

3. Combination reaction

4. Displacement reaction

Question 36.

1. A solution of substance ‘X’ is used for whitewashing. What is substance ‘X? State the chemical reaction of X’ with water.

Why does the colour of copper sulphate solution change when an iron nail is dipped in it? 
Answer:

‘X’ is calcium oxide (CaO)

CaO(s) + H₂O(l)→  Ca(OH)₂(aq) + Heat

It is because iron displaces copper from CuS04 to form FeSO₄ which is pale green

Question 37. Using a balanced chemical equation explain the difference between a displacement reaction and a double displacement reaction.
Answer:

In a displacement reaction, more reactive metal can displace less reactive metal from its salt solution

Example:  Cu(s) + 2AgNO(aq)→ Cu(NO₃)₂(aq) + 2Ag(s)

In a double displacement reaction, two compounds exchange their ions to form two new compounds,

Example: NaOH + MCI→ NaCl + H₂O

Question 38. When you have mixed the solutions of lead (II) nitrate and potassium iodide

1. What was the colour ofthe precipitate formed and can you name the precipitate?
2. Write the balanced chemical equation for this reaction.
3. Is this also a double displacement reaction?

Answer:

The colour of the precipitate is yellow. The name of the compound formed as a precipitate is lead iodide (Pbl₂).

Pb(NO₃)₂ (aq) + 2KI(aq)→ Pbl₂(s) + 2KNO₃(aq)

Yes, it is also a double displacement reaction.

Question 39. Balance the following chemical equations:

1. BaCl₂ + H₂SO₄ → BaSO₄ + HCl
2. Ca(OH)₂ + HNO₃→ Ca(NO₃)₂ + H₂O
3. Pb(NO₃)₂→ PbO + NO₂ +O₂
4. MnO₂ + HCl→MnCl₂ + H₂O + Cl₂

Answer:

1. BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl
2. Ca(OH)₂ + 2HNO₃→ Ca(NO₃)₂ + 2H₂O
3. 2Pb(NO₃)₂→ 2PbO + 4NO₂ +O₂
4. MnO₂ + 4HCl→MnCl₂ + 4H₂O + Cl₂

Question 40. Define combination reaction. Give one example ofa combination reaction which is also exothermic.
Answer:

A reaction in which two elements or compounds combine to form a single compound is called a combination reaction.

CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat

It is also an exothermic reaction because heat is evolved.

Question 41. Write the balanced chemical equations for the following reactions.

1. Sodium carbonate in reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogen carbonate.
2. Sodium hydrogen carbonate in reaction with hydrochloric acid gives sodium chloride, and water and liberates carbon dioxide.
3. Copper sulphate on treatment with potassium iodide precipitates cuprous iodide(Cu₂I₂), liberates iodine gas and also forms potassium sulphate.

Answer:

1. Na₂CO₃ + HCl → NaCl + NaHCOg
2. NaHCO₃ + HCl → NaCl + H₂O+ CO₂
3. 2CuSO₄ + 4Kl→Cu₂I₂ + 2K₂SO₄ + I₂

Question 42. A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type ofthe chemical reaction.
Answer:

KCl(aq) + AgNO₃ →AgCl(s) ↓ + KNO₃(aq)

Double displacement and precipitation reaction

Question 43. Ferrous sulphate decomposes with the evolution of gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.
Answer:

2FeSO(s) → (Heat) → 2Fe₂SO₃(s) + SO₂(g) + SO₃(g)

It is an example of a thermal decomposition reaction.

Question 44. Why do fireflies glow at night?
Answer:

Fireflies have a protein which in the presence ofan enzyme undergoes aerial oxidation.

This is a chemical reaction which involves the emission of visible light.
Therefore, fireflies glow at night.

Question 45. Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?
Answer:

Grapes when attached to the plants are living and therefore their immune system prevents fermentation. The microbes can grow in the plucked grapes and under anaerobic conditions, these can be fermented. This is a chemical change.

Question 46. Which among the following are physical or chemical changes?

1. Evaporation of petrol
2. Burning liquefied Petroleum Gas (LPG)
3. Heating of iron rod to red hot
4. Curdling of milk
5. Sublimation of solid ammonium chloride

Answer:

1. 1, 3 and 5 are physical changes.
2. 2 and 4 an’ chemical changes

Question 47. A substance X, which is an oxide of group 2 element is used intensively in the cement industry. This element is present in bones also. On treatment with water, it forms a solution which turns red litmus blue. Identify and also write the chemical reaction involved.
Answer:

The name of the substance is Calcium oxide.

CaO + H₂ (l) → Ca(OH)(aq)

Question 48. Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. Explain why1.
Answer:

Zinc is more reactive than copper.

Zn + 2HCl → ZnCl₂ + H₂

Al + HCl →   No reactions.

Question 49. A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.

1. Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.
2. Name the black substance formed and give its chemical formula.

Answer:

1. Metals such as silver when attacked by substances around it such as moisture, acids, gases, etc, are said to corrode and this phenomenon is called corrosion.
2. The black substance is formed because silver (Ag) reacts with H₂S present in the air. It forms a thin black coating of silver sulphide (Ag₂S).

Question 50. Give reasons why:

1. Sodium acts as a reducing agent while chlorine acts as an oxidising agent in the following reaction: 2Na+Cl → 2 NaCl(s)
2. White-coloured silver chloride turns grey when kept in sunlight.

Answer:

1. Sodium reduces chlorine atoms to chloride ions, therefore it acts as a reducing agent while chlorine oxidises sodium atoms to sodium ions, therefore it acts as an oxidising agent.
2. This is due to the decomposition of silver chloride into silver and chlorine by light.

Question 51. Give one example of a combination reaction in which an element combines with a new compound to give a new compound
Answer:

8NH₃ + 3Cl₂ → 6NH₄Cl + N₂

O₂ + 2SO₂ →  2SO₃

CBSE Class 10 Science Class 10 Science Chapter 1Chemical Reactions And Equations Multiple Choice Questions

Question 1. Which of the following is not a physical change?

1. Boiling of water to give water vapour
2. Melting of ice to give water
3. Dissolution of salt in water
4. Combustion liquefied Petroleum Gas (LPG)

Answer: 4. Combustion liquefied Petroleum Gas (LPG)

Question 2. The following reaction is an example ofa

4NH₃(g) + 5O₂(g)→4NO(g) + 6H₂O(g)

1. Displacement reaction

2. Combination reaction

3. Redox reaction

4. Neutralisation reaction

1. 1 and 4
2. 2 and 3
3. 1 and 3
4. 3 and 4

Answer: 4.  3 and 4

Question 3. Which of the following statements about the given reaction are correct?

3Fe(s) + 4H₂O(g) > Fe₃O₄) + 4H₂(g)

1. Iron metal is getting oxidised

2. Water is getting reduced

3. Water acts as a reducing agent

4. Water acts as an oxidising agent

1. 1, 2 and 3
2. 3 and 4
3. 1, 2 and 4
4. 2 and 4

Answer: 3. 1, 2 and 4

Question 4. Which of the following are exothermic processes?

1. Reaction of water with quick lime

2. Dilution of an acid

3. Evaporation of water

4. Sublimation of camphor (crystals)

1. 1 and 2
2. 2 and 3
3. 1 and 4
4. 3 and 4

Answer: 1. 1 and 2

Question 5. Three beakers labelled as A, B, and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous CuS04 and NaCl were added to the beakers A, B, and C respectively.  It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas in the case of beaker C, the temperature of the solution fell. Which one of the following statement(s) is (are) correct?

1. In beakers A and B, an exothermic process has occurred.

2. In beakers A and B, an endothermic process has occurred.

3. In beaker C exothermic process has occurred.

4. In beaker C endothermic process has occurred.

1. 1 Only
2. 2 Only
3. 1 and 4
4. 2 and 3

Answer: 3.  1 and 4

Question 6. A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate. The light purple colour of the solution fades and finally disappears. Which ofthe following is the correct explanation for the observation?

1. KMnO₄ is an oxidising agent, it oxidises FeSO₄
2. FeSO₄ acts as an oxidising agent and oxidises KMnO₄
3. The colour disappears due to dilution: no reaction is involved
4. KMnO₄ is an unstable compound and decomposes in the presence of FeSO₄ to a colourless compound.

Answer: 1. KMnO₄ is an oxidising agent, it oxidises FeSO₄

Question 7. Which among the following is (are) double displacement reaction(s)?

1. Pb + CuCl₂→ PbCl₂ + Cu

2. Na₂SO₄ + BaCl₂→  BaSO₄+ 2NaCl

3. C +O₂ → CO₂

4. CH₄ + 2O₂→ CO₂ + 2H₂O

1. 1 and 4
2. 2 Only
3. 1 and 2
4. 3 and 4

Answer: 2.  2 Only

Question 8. Which among the following statements) is (are) true? Exposure of silver chloride to sunlight for a long duration turns grey due to

1. The formation of silver by decomposition of silver chloride

2. Sublimation of silver chloride

3. Decomposition of chlorine gas from silver chloride

4. Oxidation of silver chloride.

1. 1 only
2. 1 and 3
3. 2 and 3
4. 4 only

Answer: 1.  1 only

Question 9. Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. This process is called slaking oflime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is (are) true about the slaking of lime and the solution formed?

1. It is an endothermic reaction

2. It is an exothermic reaction

3. The pH ofthe resulting solution will be more than seven

4. The pH ofthe resulting solution will be less than seven

1. 1 and 2
2. 1 and 3
3. 1 and 4
4. 4 only

Answer: 2.  1 and 3

Question 10. Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which ofthe following correctly represents the type ofthe reaction involved?

1. Displacement reaction

2. Combination reaction

3. Precipitation reaction

4. Double displacement reaction

1. 1 only
2. 2 only
3. 4 only
4. 2 and 4

Answer: 4.  2 and 4

Question 11. Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during the electrolysis of water is

1. 1:1
2. 2: 1
3. 4:1
4. 1:2

Answer: 2.  2: 1

Question 12. Which ofthe following is(are) an endothermic process(es)?

1. Dilution of sulphuric acid

2. Sublimation of dry ice

3. Condensation of water vapours

4. Evaporation of water

1. 1 and 3
2. 2 only
3. 3 only
4. 2 and 4

Answer: 4.  2 and 4

Question 13. In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which ofthe following can be used in place of lead nitrate?

1. Lead sulphate (insoluble)
2. Lead acetate
3. Ammonium nitrate
4. Potassium sulphate

Answer: 2.  Lead acetate

Question 14. Which of the following gases can be used for storage of fresh samples of oil for a long time?

1. Carbon dioxide or oxygen
2. Nitrogen or oxygen
3. Carbon dioxide or helium
4. Helium or nitrogen

Answer: 4.  Helium or nitrogen

Question 15. The following reaction is used for the preparation of oxygen gas in the laboratory

3Fe(s) + 4H₂ O(g)→ Fe₃ O₄ (s) + 4H₂ (g)

Which of the following statement (s) is(arc) correct about the reaction?

1. It is a decomposition traction and endothermic
2. It is u i’ombinntion traction
3. It is (i decomposition reaction accompanied by the release of heat
4. It is a photochemical decomposition reaction and exothermic

Answer: 1.  It is a decomposition traction and endothermic

Question 16. Which one ofthe following processes involves chemical reactions?

1. Storing ofoxygen gas under pressure in a gas cylinder
2. Liquefaction ofair
3. Keeping petrol in a china dish in the open
4. Heating copper wire in presence ofair at high temperature

Answer: 4.  Heating copper wire in the presence ofair at high temperature

Question 17. In which of the following chemical equations, do the abbreviations represent the correct states ofthe reactants and products involved at reaction temperature?

1. 2H₂(l) + O₂(Z)→2H₂O(g)
2. 2H₂(g) +O₂(l) → 2H₂O(l)
3. 2H₂(g) + O₂(g)→ 2H₂O(l)
4. 2H₂(g) + O₂(g)→ 2H₂O(g)

Answer: 3.  2H₂(g) + O₂(g)→ 2H₂O(l)

Question 18. Which of the following are combination reactions?

1. \(2 \mathrm{KCIO}_3 →{\text { Heat }}→ 2 \mathrm{KCI}+30_2\)

2. \(\mathrm{MgO}+\mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{Mg}(\mathrm{OH})_2\)

3. \(4 \mathrm{Al}+3 \mathrm{O}_2 \longrightarrow 2 \mathrm{Al}_2 \mathrm{O}_3\)

4. \(\mathrm{Zn}+\mathrm{FeSO}_4 \longrightarrow \mathrm{ZnSO}_4+\mathrm{Fe}\)

1. 1 and 3
2. 3 and 4
3. 2 and 4
4. 2 and 3

Answer: 4.  2 and 3

Question 19. Which ofthe statements about the reaction below are incorrect?

2PbO(s) + C(s)→ 2Pb(s) + CO₂(g)

1. Lead is getting reduced.

2. Carbon dioxide is getting oxidised.

3. Carbon is getting oxidised.

4. Lead oxide is getting reduced.

1. 1 and 2
2. 1 and 3
3. 1, 2 and 3
4. All

Answer: 1 and 2 are incorrect.

Question 20. Fe₂O₃ + 2Al  → Al₂O₃ + 2Fe

The above reaction is an example of a:

1. Combination reaction
2. Double displacement reaction
3. Decomposition reaction
4. Displacement reaction

Answer: 4. Displacement reaction

Question 21. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.

1. Hydrogen gas and iron chloride are produced.
2. Chlorine gas and iron hydroxide are produced.
3. No reaction takes place.
4. Iron salt and water are produced.

Answer: 1. Hydrogen gas and iron chloride are produced.

CBSE Class 10 Science Chapter 9 Heredity And Evolution

Heredity:

CBSE Class 10 Science Chapter 9 Heredity And Evolution Short Question And Answers

Question 1. If trait A exists in 10% of a population of an asexually reproducing species and trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Answer: Trait B has arisen earlier.

Read and Learn More CBSE Class 10 Science Short Answer Questions

Question 2. How does the creation of variations in a species promote survival?
Answer:

Variations occur in a species due to inaccurate copying of DNA and also due to sexual reproduction. Depending on the nature of variations, different individuals would have different kinds of advantages.

• For example, bacteria variants which can withstand heat have better chances to survive in a heat wave than non-variant bacteria that cannot tolerate heat waves.
• Thus, variations in the population of a species help in the survival of a species. However, at the individual level, variants which are not suitable to the prevailing environment may not survive.

Question 3. How do Mendel’s experiments show that traits may be dominant or recessive?
Answer:

The trait which appears in all the members of the F₁ generation and also in 75% of members of the F₂ generation, obtained by self-fertilisation of the F₁ generation, is the dominant character.

The trait which does not appear in the F₁ generation but after self-fertilisation of the F₁ generation reappears in 25% of the F₂ generation is known as recessive character.

Question 4. How do Mendel’s experiments show that traits are inherited independently?
Answer:

If pea plants with two different pairs of characteristics (e.g., tall dwarf and round seeds/ wrinkled seeds) are bred with each other, the F, progeny would have all tall plants with round seeds.

• This implies that round seed is a dominant character over wrinkled seed. In F2 progeny there would be some tall plants with round seeds and short plants with wrinkled seeds.
• However, there would be some plants with mixed characteristics plants with wrinkled seeds and short plants with rough seeds.

This depicts that tall/dwarf traits and round/wrinkled traits are inherited independently of each other (law of independent assortment). The following Punnett square explains this:

Parents: TTRR × torr

F₁: Tt Rr

F₂:

Phenotypic ratio: Tall round: Tall wrinkled: Dwarf round: Dwarf wrinkled = 9:3:3:1 3.

Question 5. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits group A or O is dominant? Why or why not?
Answer:

The information is not enough to infer which trait, blood group A or O, is dominant.

Reason:

1. If A is considered to be dominant over O, then possible combinations are— Male AO and Female OO.
   1. Thus, the daughter can be OO and hence has blood group O.
2. If O is supposed to be dominant over A then the following combinations are possible- Male AA and Female OO or OA.

In this case, the daughter can be OA and hence has blood group 0.

Thus, from the information given, we cannot ascertain which blood group is dominant.

Question 6. How is the sex of the child determined in human beings?
Answer:

The sex of the child in human beings is genetically determined. All children inherit X sex chromosomes from their mothers regardless of whether they are boys or girls.

The sex of the children is determined by what sex chromosome they inherit from their father. A child who inherits an X chromosome from a father would be a girl, and one who inherits a Y chromosome from a father would be a boy.

Question 7. What are the different ways in which individuals with a particular trait may increase in a population?
Answer:

The different ways in which individuals with a particular trait may increase in a
population are:

1. Natural selection of some variants: Natural selection provides chances for certain variations that are suitable to changing environments.
2. Genetic drift: Accidents/migration of members of a small population also cause an increase in individuals having particular traits. However, genetic drift does not provide a survival advantage.

Question 8. Why are traits acquired during the lifetime of an individual, not inherited?
Answer:

Changes that occur in germ cells and DNA are only transmitted from one generation to the next generation. Changes/traits in non-reproductive tissues acquired in a lifetime are not passed to the next generation.

Question 9. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer:

• The small number of members in a population of tigers does not allow a large number of variations to occur which are essential to the survival of the species.
• A deadly disease or calamity may cause the death of all the tigers. The small number of tigers also indicates. that existing tiger variants are not well adapted to the existing environment and may extinct soon.

Question 10. What factors could lead to the rise of a new species?
Answer:

The factors that can lead to the rise of a new species are:

1. Natural selection.
2. Changes in several chromosomes or changes in genes/genes.
3. Geographical isolation.
4. Reproductive isolation.

Question 11. Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Answer:

No, because geographical isolation does not affect much in asexually reproducing organisms. Asexually reproducing organisms pass on the parent DNA to offspring leaving no chance of speciation.

However, geographical isolation works as a major factor in cross-pollinated species, as it would result in the accumulation of variation in the two geographically separated populations.

Question 12. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer:

No, asexually reproducing organisms have very little variation over generations. Any change resulting from geographical isolation may not be passed on to the next generation. These variations in DNA are not enough to raise a new species.

Question 13. Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer:

1. Feathers in some ancient reptiles like dinosaurs, as fossils indicate, evolved to provide insulation in cold weather. However, they cannot fly with these feathers. Later on, birds adapted the feathers to flight. This means that birds are very closely related to reptiles since dinosaurs were reptiles.
2. Another method to find out how close two species are in evolutionary terms is by comparing the DNA of different species. It provides a direct estimate of how much the DNA has changed during the formation of the new species.

Question 14. Can the wings of a butterfly and the wings of a bat be considered homologous organs? Why or why not?
Answer:

No, because the wings of the bat are entirely different in respect of structure, origin and plan from the wings of a butterfly. Wings of bats are modified fore-limbs which have bones and skin, whereas the wings of butterfly do not have bones.

However, wings in both species perform similar functions, so they are analogous organs and not homologous organs

Question 15. What are fossils? What do they tell us about the process of evolution?
Answer:

Preserved remains and imprints of ancient plants and animals are called fossils. Fossils tell us about the following:

1. Organisms that lived long ago.
2. The structure of ancient organisms and the period during which they lived.
3. Evolutionary relations among organisms.
4. The organisms become more complex in the upper strata when compared to the lower strata. It indicates the evolutionary process.
5. Connecting links between different species. For example, Archaeopteryx exhibits an intermediate link between reptiles and birds.

Question 16. Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?
Answer:

Although the genetic makeup of humans may be slightly different in different races of people, there is no reproductive isolation. Different species cannot breed and produce fertile progeny.

In the case of human beings, individuals different in size, colour and looks can marry among themselves and produce fertile offspring. So, they are clubbed in the same species Homo sapiens.

Question 17. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
Answer:

Evolution does not mean progress. Evolution causes the generation of diversity and the shopping of diversity by environmental selection. Due to evolution, more and more complex body designs have emerged over time and this has been considered a progressive trend.

• It does not mean older and simpler body designs are inefficient and complex body designs like spiders, fish and chimpanzees have better body designs. Many of the older and simpler body designs still survive.
• For example, bacteria have simpler body forms, and are found in the most inhospitable habitats like hot springs, deep sea and the ice in Antarctica.
• Thus, bacteria, spiders, fish and chimpanzees are simple species in the teaming spectrum of evolving life. All the organisms which exist have a body design that is good as it is suited to their environment.

Question 18. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Answer:

The information given in the question is not sufficient to infer that the light eye colour trait is dominant or recessive.

Reason: It is just possible that the parents are homozygous for the light eye colour trait. Even though it is a recessive trait, it has appeared in all of their children. Both of the parents contributed the same recessive allele.

Question 19. How are the areas of study evolution and classification—interlinked?
Answer:

• Evolutionary relationships are traced in the classification of organisms. For the classification of organisms, we look for similarities among organisms which allows us to group them. The more characteristics two species will have in common, the more closely they are related.
• It indicates that the more closely two species are related, the more recently they would have had a common ancestor. Thus, the classification of species is a reflection of their evolutionary relationship.

Question 20. Explain the terms analogous and homologous organs with examples.
Answer:

1. Analogous organs: The organs which perform similar functions in different organisms but are different in structure and origin are called analogous organs For example, the wings of a bird and the wings of an insect.
2. Homologous organs: The organs which perform different functions in different organisms but have similar structure, origin and components, are called homologous organs. For example, the forelimbs of a frog, the front legs of a horse, the wings of a bird, hands of human beings (all are modified forelimbs performing different functions).

Question 21. Outline a project which aims to find the dominant coat colour in dogs.
Answer:

1. Select a black homozygous male dog and a white homozygous female dog. Allow them to mate. Observe their progeny (F₁ generation).
2. If all members of the F₁ generation have black coats, then the black colour coat is dominant. If the progeny has a white coat then a white colour coat is dominant.

Question 22. Explain the importance of fossils in deciding evolutionary relationships.
Answer:

Fossils provide us evidence about:

1. The organisms that lived long ago such as the period during which they lived, their structure etc.
2. Evolutionary development of species i.e., line of their development (phylogeny of organisms).
3. Connecting links between two groups. For example, feathers present in some dinosaurs (reptiles) means that birds are very closely related to reptiles.
4. Which organisms evolved earlier and which later?
5. Development of complex body designs from simple body designs.

Question 23. What evidence do we have for the origin of life from inanimate matter?
Answer:

Experiments conducted by Stanley L. Miller and Harold C. Urey in 1953 provide some light on the origin of life from inanimate matter.

• They assembled an atmosphere similar to that thought to exist on early Earth (that had molecules like ammonia (NH₃), methane (CH₄) and hydrogen sulphide but no oxygen) over water.
• They maintained the mixture of these gases just below 100°C and passed sparks to simulate lightning.
• At the end of a week, 15% of the carbon (from methane) had been converted to simple compounds of carbon including amino acids which make up protein molecules.
• It indicates the possibility of the origin of life from inanimate matter on the earth, when the atmosphere was reducing (containing no free oxygen), containing gases like methane, ammonia, and hydrogen sulphide; frequent lightning and enough water was present.
• Simple amino acids which are building blocks of proteins might have given rise to complex molecules that are building blocks of cells.

The origin of life from inanimate matter is not at all possible today because:

1. The atmosphere contains free oxygen (oxidising) which causes breakdown of molecules necessary for the origin of life.
2. The conditions which existed on early Earth cannot be regenerated.

Question 24. Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?
Answer:

Sexual reproduction causes more viable variations due to the following reasons:

1. Error in copying of DNA, which is not highly significant.
2. Random segregation of paternal and maternal chromosomes at the time of gamete formation.
3. Exchange of genetic material between homologous chromosomes during formation of gametes.
4. Accumulation of variations occurred due to sexual reproduction over generation after generation and selection by nature created wide diversity.

In the case of asexual reproduction, only very small changes due to inaccuracies in DNA copying pass on to progeny. Thus, offspring of asexual reproduction are more or less genetically similar to their parents.

So, it can be concluded that evolution in sexually reproducing organisms proceeds at a faster pace than in asexually reproducing organisms.

Question 25. How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer:

When round and green seeded crossed with wrinkled and yellow seeded pea plants, F₁ generation has obtained round and yellow seeds. F₁ generation when self-fertilised shows four types of plants:

1. Round and yellow
2. Wrinkled and yellow
3. Round and green
4. Wrinkled and green.

If we interpret this result that indicates both parents must be contributing equally to the DNA of the progeny during sexual reproduction.

If both parents can help determine the trait in the progeny, both parents must be contributing a copy of the same gene. It means a member of progeny must have two sets of all genes, one inherited from each parent.

Question 26. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?
Answer:

No, it depends on the nature of variations, different individuals have different kinds of advantages. When drastic changes occur in the environment only those organisms of the population will survive which have favourable variations.

Question 27. Variations are important for the survival of species over time. Justify this statement with reasons.
Answer:

1. It causes adaptations.
2. It promotes natural selection.

Question 28.

1. Which type of organs are shown in the figure below?
2. Which type of origin and structure do these organs have?

Answer:

1. These are organs which help in flying (wings of insects and wings of birds).
2. The structure and components of these wings are different. They look similar because they have a common use for flying, but their origins are not common, i.e., they are analogous.

Question 29. Define F₁ and F₂ generations.
Answer:

F₁ or first filial generation is the generation of hybrids derived from a cross between two genetically different homozygous individuals.

F₂ or second filial generation is the generation produced as a result of interbreeding between individuals of the F₁ generation.

Question 30. “It is a matter of chance whether a couple will give birth to a male child or a female child.” Justify this statement with the help of a flow chart showing the fusion of sex chromosomes.
Answmgmg

Since the sperms carry an ing ‘X’ chromosome and sperms carry an ing Y chromosome have an ave equal/50-50 chance of fertilizing an egg, thus it is a matter of chance whether a couple will give birth to a male or a female child.

Question 31. What function is performed by human arms, the forelimbs of dogs and the forelimbs of whales?

1. Which type of organs are these?
2. Why do we call them so?

Answer:

1. Human arm: holding things Forelimbs of dog: running Forelimbs of whales: paddles
2. Homologous
3. Same origin, and different functions.

Question 32.

1. How many gene sets should a germ cell have?
2. Mention two factors causing evolution.

Answer:

1. One gene set
2. 1. Reproduction isolation
   2. Natural selection

Question 33.

1. “Recent fossils are found closer to the earth’s surface.” Comment on the statement state the ing reason.
2. List two factors which could lead to the rise of new species.

Answer:

1. This statement is correct as the fossils found closer to the surface of the earth are more recent and those found in deeper layers are older ones.
2. Natural selection and genetic drift.

Question 34. “Experiences of an individual during its lifetime cannot be passed on to its cannot direct evolution”. Justify this statement ent giving an example.
Answer:

Since acquired characteristics are not inherited over generations, changes in non-reproductive tissues cannot be passed on to the DNA of the germ cells.

Question 35. In a monohybrid cross between tall pea plants denoted by TT and short pea plants denoted by tt, Sehaj Anant obtained only tall plants denoted by Tt in the F₁ generation. However, in the F₂ generation, she obtained both tall and short plants. Using the above information explain the law of dominance.
Answer:

According to the law of dominance, the dominant trait gets expressed in the F, generation.

Although both the dominant and the recessive traits get inherited in the F generation, it is only the dominant trait which gets expressed, i.e., a single copy of the dominant trait is enough for the expression of the tall traits traitrait like “T’ is thus cala-led dominant trait.

Question 36. If YYRR is Round yellow, what do the following represeyouryyyyyRR
Answer

1. your – Wrinkled, green eye – Round, green seeds

Question 37. What is the importance of DNA copying in reproduction? Why is variation beneficial to the species but not necessary for the individual? Explain.
Answer:

DNA copying is an essential part of reproduction because it ensures that the same blueprint of the body design is maintained. Variation for the species is beneficial for adaptation and better survival. It may result in new species formation.

Question 38. If a population of red beetles, living on green bushes, is being eaten by crows. During sexual reproduction, a green beetle is found in progeny:

1. What is the future of new traits?
2. Will it survive in the new habitat?

Answer:

1. Among progeny, when a green beetle is found, it escapes the attack of crows as it merges with a green colour. Green beetles increased, red decreased.
2. traitsrait will survive.

Question 39. An angiosperm plant having red coloured flowers when crossed with the other having the same colour produced 40 progenies, out of which 30 plants were with red coloured flowers, and 10 plants were with white coloured flowers. Find out:

1. What is the possible genotype of parent plants?
2. Which trait is dominant and which is recessive?
3. What is this cross called and what is its phenotypic ratio? 

Answer:

1. Rr and Rr.
2. The red colour of the flower is the dominant trait while the white colour is the recessive trait.
3. Monohybrid cross, phenotypic ratio is 3: 1.

Question 40. The modern human beings have originated in Africa.

1. What evidence suggests this fact?
2. If an animal is similar to its ancestors, what does it imply?

Answer:

1. Discovery of fossils in AfriOrganismsnism is recently evolved fancestorsstAnimalsimal has not accumulated variations.

Question 41.

1. What is the genetic constitution of human sperm?
2. Mention chromosomeomes pair present in zygote determining the sex of a male child.

Answer:

1. 22+ Y or 22+ X
2. (22 + Y + 22+ X)

Question 42.

1. Wrthe ite full form of DNA.
2. Why are variations essential for the species?

Answer:

1. Deoxyribonucleic Acid
2. For survival.

Question 43. Where are the genes located? What is the chemical nature of genes?
Answer:

Genes are located on chromosomes in linear sequence and at fixed positions. Chemically, genes are accurate since they are nucleic acids which constitute DNA.

Question 44.

1. In a monohybrid cross between tall pea plants denoted by TT and short pea plants denoted by tt, Preeti obtained only tall plants denoted by Tt in the F₁ generation. However, in the ₂ generations, she obtained both tall and short plants. Using the above information explain the law of dominance.
2. What is genetic drift?

Answer:

1. According to the law of dominance trait that is dominant gets expressed in the F₁ generation. Although both the dominant and the recessive traits get inherited in the F₁ generation, it is only the dominant trait which gets expressed, i.e., a single copy of the dominant trait is enough for the expression of the tall trait. Traits like “T” are thus called dominant traits.
2. Accidents in a small population can change the frequency of some genes in a population although they give no survival advantage. This is called genetic drift.

Question 45. Differentiate between:

1. Homologous organs and Analogous organs
2. Pollination and Fertilisation
3. What do fossils tell us about the process of evolution?

Answer:

1. Organs in different organisms have the same origin with different functions/differoriginsigin, same function.
2. Transfer of pollen from the stamen to the pistil of the flower/Fusion of male and female gametes.
3. Help in establishing links and act as evidence of evolution.

Question 46.

1. Place the following in the correct sequence: Natural selection / Migration/New species/ Gene flow.
2. Evolutions of cauliflower, broccoli, cabbage ge, and red cabbage are all forms of wild cabbage. Is this an example of natural selection or artificial selection?

Answer:

1. Migration/Gene flow/Natural selection/New species.
2. Artificial selection.

Question 47.

1. State any two factors that could lead to the rise of a new species.
2. How do analogous organs provide evidence in favour of evolution?

Answer:

1. Natural Selection, Genetic drift, Mutations, Variations.
2. The organs which are similar in function but are structurally different suggest that although these two organs may look alike superficially giving an idea of common ancestry the difference in structure and origin suggests that organisms having these organs have a distant ancestor but such organs have developed during evolution as an adaptation to a similar mode of life.

Question 48.  In plants round seed is dominant over the wrinkled. If a cross is carried between these two plans answer the following questions:

1. Mention the genes for the traits of parents.
2. State the trait of F₁ hybrids.
3. Write the ratio of F₂ progeny obtained from this cross. What is the name of the cross?

Answer:

1. R/rr
2. Rr/hybrid Round

3:1

1:2:1

Monohybrid cross.

Question 49.

1. State the term given to the structure shown in figures given b.low.
2. State the evolutionary evidence obtained from such structures.
3. Why are traits acquired during the lifetime of an individual, not inherited

Answer:

1. Homologous orgaThe basic structures of limbs same, but function differently.
2. The similarities indicate that all these vertebrates had common ancestors.
3. Change in non-reproductive tissues cannot be passed to germ cells.

Question 50.

1. Name the scientist who worked out the rules of inheritance.
2. Mention any two strategies that are used by different species for determine ing sex of their newborns.

Answer:

1. Mendel
2. Some rely on environmental cues. In some ani, mals the temperature at which a fertilized egg is kept determines its sex. In snails, individuals can change sex, indicating that sex is not genetically determined.

Question 51. Give appropriate terms for the following:

1. The trait which can express itself in the next generation.
2. The trait an organism has due to inheritance.
3. Origin of a new species from a pre-existing one.

Answer:

1. Dominant trait
2. Inherited trait
3. Speciation

Question 52.

1. What are fossils?
2. Explain the importance of fossils in evolutionary relationship

Answer:

1. Impressions of the body parts of the organisms and preserved traces of the living organisms are called fossils.
2. The presence of fossilized remains of the organisms is the evidence of existence of organisms millions of years ago which have now become extinct. Fossils also help in determining the connecting links between various groups and their origin from their primitive ones.

Question 53.

1. Name the scientist who gave the idea of the evolution of species by natural selection.
2. What conclusion did Mendel draw from his experiments about traits?
3. Arrange the following according to evolution.

Cockroach, Mango tree, Gorilla, Fish

Answer:

1. Darwin.
2. Traits are inherited independently.
3. Mango tree-Cockroach-Fish-Gorilla.

Question 54.

1. Explain why the wing of a bat and the wing of a bird are considered to be analogous organs
2. List two factors that lead to the formation of a new species.

Answer:

1. Design, structure and components are different. Origins are not common.
2. Genetic drift and natural selection.

Question 55. How do different races of human beings belong to the same species?
Answer:

• By using various tools such as excavation, time-dating and studying fossils as well as determining DNA sequences to study human evolution, it is evident that there is no biological basis to the notion of the human race. All humans are a single species.
• It is established by scientific studies that all human races belong to a human species called Homo sapiens. That een evolved in Africa and spread across the world in stages.

Question 56. How is the sex of a newborn determined in humans?
Answer:

The sex of the individual is genetically determined i.e., genes inherited from parents decide whether the newborn will be a boy or a girl. A newborn who inherits an ‘X’ chromosome fa from a father will be a girl and one who inherits a Y chromosome from a father will be a boy.

Question 57. Does the genetic combination of mothers play a significant role in determining the sex of a newborn?
Answer:

No, because mothers have a pair of X chromosomes. All children will inherit an ‘X’ chromosome from their mother regardless of whether they are boys or girls.

Question 58. Mention three important features of fossils which help in the study of evolution.
Answer:

1. Fossils represent modes of preservation of ancient species.
2. Fossils help in establishing evolutionary traits among organisms and their ancestors.
3. Fossils help in establishing the period in which organisms lived.

Question 59. Why do all the gametes formed in human females have an X chromosome?
Answer:

Human females have two X chromosomes called sex chromosomes. During meiosis at the time of gamete formation, one X chromosome enters each gamete. Hence all the gametes possess an X chromosome.

Question 60. In human beings, the statistical probability of getting either a male or a female child is 50:50. Give a suitable explanation.
Answer:

The sex of an infant is determined by the type of sex chromosome contributed by the male gamete. Since the ratio of male gametes containing the X chromosome and those containing the Y chromosome is 50: 50, the static probability of male or female infant is 50: 50.

Question 61. A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.
Answer:

Fewer individuals in a species impose extensive inbreeding among them. This limits the appearance of variations and puts the species at a disadvantage if there are changes in the environment. Since the individuals fail to cope with the environmental changes, they may become extinct.

Question 62. What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?
Answer:

Structures which have a common basic structure but perform different functions are called homologous structures, e.g. fore-limbs of reptiles, amphibians and mammals. Yes, they have a common ancestor but they are variously modified to carry out different activities.

Question 63. Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
Answer:

• Though animals have a vast diversity in structures they probably do not have a common ancestry, because common ancestry may greatly limit the extent of diversity.
• As many of these diverse animals are inhabiting the same habitat, their evolution by geographical isolation and speciation is also not likely. Thus, a common ancestry for all the animals is not the likely theory.

Question 64. Give the pair of contrasting traits of the following characters in the pea plant and mention which is dominant and recessive

1. Yellow seed
2. Round seed

Answer:

Question 65. Why did Mendel choose the pea plant for his experiments?
Answer:

1. Easy to grow
2. Short life span
3. Easily distinguishable character larger gear size of flower
4. Self-pollinated

Question 66. A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.
Answer:

1. The woman produces ova with ‘X’ chromosome.
2. The man produces sperm with X and Y chromosomes which determines the sex of the baby.

Question 67. What are the three ways which can produce variant genotypes in the environment?
Answer:

1. Gene mutations
2. Crossing over
3. Hybridisation

Question 68. Give reasons for the appearance of new combinations of characters in the F₂ progeny.
Answer: The tall/short and round/wrinkled seed traits are independently inherited.

Question 69. The genotype of green stemmed tomato plant is denoted as GG and that of purple stemmed tomato plant as gg. When are these two crossed?

1. What colour of stem would you expect in their F₁ progeny?
2. Give the percentage of purple-stemmed plants if F₁ plants are self-pollinated.
3. In what ratio would you find the genotypes GG and Gg in the F₂ progeny?

Answer:

1. Green (as G denotes the dominant gene and is expressed in all plants of F₁ generation.)
2. 25% of F₂ generates ions raised by self-pollinated F plants.
3. GG-25%

Gg-50%

Thus, the ratio is 1:2 in F₂ progeny.

Question 70. Guinea pigs having black colour when crossed with guinea pigs having the same colour produced 80 offspring, out of which 60 were black and 20 were white. Now, find out:

1. What is the possible genotype of the guinea pig?
2. Which trait is dominant and which trait is recessive?
3. What is this cross called and what is its phenotypic ratio?

Answer:

1. Bb x Bb
2. Black is dominant while white is recessive.
3. Monohybrid cross Phenotypic ratio = 3:1

Question 71. In a quarry of sandstone, a digger found some bones below the rocks. He took them out and was about to throw them away when his fellow digger told him that this could be a fossil and they should hand it over to the museum.

Answer the following questions based on the above situation:

1. Which values are promoted by the fellow digger?
2. What contributions are the diggers making to the scientific world?
3. Imagine yourself to be the person in the museum whom the diggers approach. What would be your response to the diggers’ discovery?

Answer:

1. Rational thinking, awareness, preservation of heritage.
2. They provided a link which can help scientists to study the process of evolution and know more about the world, in which humans did not exist.
3. I would take the bone samples and send them for carbon dating to find which period they belong to.

Question 72. A group of class X students prepared a street play to educate ate masses on gender disparity to the top sex determination of a girl child and abort it.

1. In human beings, what is the chance of giving birth to a girl child?
2. Who is responsible for the birth of a female child and why?
3. What value is depicted among the group members of class X?

Answer:

1. The chance of giving birth to a girl child is 5The male-male is responsible because only the male individual is a carrier of X and X chromosomes.
2. The group members show teamwork, collaborative leadership and participating citizenship.

Heredity And Evolution Multiple Choice Questions

Question 1. The exchange of genetic material takes place in

1. Vegetative reproduction
2. Asexual reproduction
3. Sexual reproduction
4. Budding

Answer: 3. Sexual reproduction

Question 2. Two pink-coloured flowers on crossing resulted in 1 red, 2 pink and 1 white flower progeny. The nature of the cross will be

1. Double fertilisation
2. Self-pollination
3. Cross fertilisation
4. No fertilisation

Answer: 2. Self-pollination

Question 3. A cross between a tall plant (TT) and a short pea plant (tt) resulted in progeny that were all tall plants because

1. Tallness is the dominant trait
2. Shortness is the dominant trait
3. Tallness is the recessive trait
4. The height the  of pea plant is not governed by gene ‘T’ or ‘t’

Answer: 1. Tallness is the dominant trait

Question 4. Which of the following statements is incorrect?

1. For every hour, mone there is a gene.
2. For every pro, then there is a gene.
3. For the production of every enzyme, there is a gene.
4. For every molecule of, fat there is a gene.

Answer: 4. For every molecule of fat there is a gene.

Question 5. If a round, green-seeded pea plant (RRyy) is crossed with a wrinkled, yellow-seeded pea plant (rrYY), the seeds produced in the F₁ generation are

1. Round and yellow
2. Round and green
3. Wrinkled and green
4. Wrinkled and yellow

Answer: 1. Round and yellow

Question 6. In human males, all the chromosomes are paired perfectly except one. This / these unpaired chromosome is/are

1. large chromosome
2. small chromosome
3. Y-chromosome
4. X-chromosome

1. 1 and 2
2. 3 only
3. 3 and 4
4. 2 and 4

Answer: 3. 3 and 4

Question 7. The maleness of a child is determined by

1. The X chromosome in the zygote
2. The Y chromosome in zygote
3. The cytoplasm of germ cell determines the sex
4. Sex is determined by chance

Answer: 2. The Y chromosome in a zygote

Question 8. A zygote which has an X-chromosome inherited from the father will develop into a

1. Boy
2. Girl
3. X-chromosome does not determine the sex of a child
4. Either boy or girl

Answer: 2. Girl

Question 9. Select the incorrect statement

1. The frequency of certain genes in a population changes over several generations resulting in the evolution
2. Reduction in weight of the organism due to starvation is genetically controlled
3. Low-weight parents can have heavy-weight progeny
4. Traits which are not inherited over generations do not cause evolution

Answer: 2. Reduction in weight of the organism due to starvation is genetically controlled

Question 10. New species may be formed if

1. DNA undergoes significant changes in germ cells
2. Chromosome number changes in the gamete
3. There is no change in the genetic material
4. Mating does not take place

1. 1 and 2
2. 2, 3 and 4
3. 1 and 3
4. 1, 2 and 3

Answer: 1. 1 and 2

Question 11. Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds produce F₁ progeny that have round, yellow (RrYy) seeds. When F₁ plants are selfed, the F₂ progeny will have a new combination of characters. Choose the new combination from the following

1. Round, yellow
2. Round, green
3. Wrinkled, yellow
4. Wrinkled, green

1. 1 and 2
2. 1 and 4
3. 2 and 3
4. 1 and 3

Answer: 2. 1 and 4

Question 12. A basket of vegetables contains carrots, potatoes, radishes and tomatoes. Which of them represent the correct homologous structures?

1. Carrot and potato
2. Carrot and tomato
3. Radish and carrot
4. Radish and potato

Answer: 3. Radish and carrot

Question 13. Select the correct statement

1. Tendril of a pea plant and phylloclade of Opuntia are homologous
2. The Tendril of a pea plant and the phylloclade of Opuntia are analogous
3. Wings of birds and limbs of lizards are analogous
4. Wings of birds and wings of bats are homologous

Answer: 1. Tendril of a pea plant and phylloclade of Opuntia are homologous

Question 14. If the fossil of an organism is found in the deeper layers of the earth, then we can predict that

1. The extinction of organisms has occurred recently
2. The extinction of organisms occurred thousands of years ago
3. The fossil position in the layers of the earth is not related to its time of extinction
4. The time of extinction cannot be determined

Answer: 2. The extinction of organism has occurred thousands of years ago

Question 15. Which of the following statements is not true concerning variation?

1. All variations in a species have an equal chance of survival
2. Change in genetic composition results in variation
3. Selection of variants by environmental factors forms the basis of evolutionary processes
4. Variation is minimal in asexual reproduction

Answer: 1. All variations in a species have an equal chance of survival

Question 16. A trait in an organism is influenced by

1. Paternal DNA only
2. Both maternal and paternal DNA
3. Maternal DNA only
4. Neither by paternal nor by maternal DNA

Answer: 3. Maternal DNA only

Question 17. Select the group which shares the maximum number of common characters

1. Two individuals of a species
2. Two genera of a family
3. Two species of a genus
4. Two genera of two families

Answer: 1. Two individuals of a species

Question 18. According to the evolutionary theory, the formation of a new species is generally due to

1. Sudden creation by nature
2. Accumulation of variations over several generations
3. Clones formed during asexual reproduction
4. Movement of individuals from one habitat to another

Answer: 2. Accumulation of variations over several generations

Question 19. From the list given below, select the character which can be acquired but not inherited

1. Colour of eye
2. Colour of skin
3. Size of body
4. Nature of hair

Answer: 3. Size of body

Question 20. The two versions of a trait (character) which are brought in by the male and female gametes are situated on

1. Copies of the same chromosome
2. Two different chromosomes
3. Sex chromosomes
4. Any chromosome

Answer: 1. Copies of the same chromosome

Question 21. Select the statements that describe the characteristics of genes

1. Genes are specific sequences of bases in a DNA molecule
2. A gene does not code for proteins
3. In individuals of a given species, a specific gene is located on a particular chromosome
4. Each chromosome has only one gene

1. 1 and 2
2. 1 and 3
3. 1 and 4
4. 2 and 4

Answer: 2. 1 and 3

Question 22. In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F₂ is

1. 1:3
2. 3:1
3. 1:1
4. 2:1

Answer: 3. 1:1

Question 23. The number of pair(s) of sex chromosomes in the zygote of humans is

1. One
2. Two
3. Three
4. Four

Answer: 1. One

Question 24. The theory of the evolution of species by natural selection was given by

1. Mendel
2. Darwin
3. Morgan
4. Lamarck

Answer: 2. Darwin

Question 25. Some dinosaurs had feathers although they could not fly but birds have feathers that help them to fly. In the context of evolution, this means that

1. Reptiles have evolved from birds
2. There is no evolutionary connection between reptiles and birds
3. Feathers are homologous structures in both organisms
4. Birds have evolved from reptiles

Answer: 4. Birds have evolved from reptiles

Question 26. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic makeup of the tall parent can be depicted as

1. TTWW
2. TTww
3. TtWW
4. TtWw

Answer: 3. TtWW

Question 27. An example of homologous organs is

1. Our arm and a dog’s foreleg.
2. Our teeth and an elephant’s tusks.
3. Potato and runners of grass.
4. All of the above.

Answer: All of the above.

Question 28. In evolutionary terms, we have more in common with

1. A Chinese schoolboy.
2. A chimpanzee.
3. A spider.
4. A bacterium.

Answer: A Chinese schoolboy.

Hint: A Chinese schoolboy is a Homo sapien like us.