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CBSE Class 10 Science Chapter 5 Periodic Classification Of Elements Very Short Answer Questions

Question 1. Where would you expect to find the element with atomic number 18 in the periodic table?
Answer: An element with atomic number 18 will lie in the 18th group and the 3rd period of the periodic table

Question Who classified the elements based on fundamental properties of elements like atomic mass?
Answer: Mendeleev.

Question 3. An element X’ belongs to the second group of the periodic table. What is the formula of sodium chloride?
Answer: XCl₂.

Question 4. State modern periodic law of classification of elements.
Answer: The properties of elements are a periodic function of their atomic number.

Question 5. Name the elements present in the first period.
Answer: Hydrogen and Helium.

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Question 6. An element has the atomic number 16. To which group and period does it belong?
Answer:

K – 2

L – 8

M – 6

A(16) = 2, 8, 6

Period = 3rd

Group = 10 + 6

= 16.

Question 7. Out of and K, which will have a stronger metallic character and why? 
Answer:

Potassium (K) will have a stronger metallic character than lithium (Li) because as we move from top to bottom in a group, the size increases, which increases the ease of liberation of electrons.

Question 8. Write the atomic number of two elements X’ and ‘Y’ having electronic configurations of 2, 8, 2 and 2, 8, 6 respectively.
Answer:

X -12(2 + 8 + 2)

Y- 16 (2 + 8 + 6)

Question 9. A metal ‘M’ belongs to the 13th group in the modern periodic table. Write the valency of the metal.
Answer:

The valency of the metal is 3.

Question 10. Chlorine, bromine, and iodine from a Dobereiner’s triad. The atomic masses of chlorine and iodine are 35.5 and 126.9 respectively. Predict the atomic mass of Bromine.
Answer:

Atomic mass = \(\frac{35.5+126.9}{2}\)

= \(\frac{162.4}{2}\)

= 81.2

Question 11. Find the atomic number of the element whose electronic configuration is 2, 8, 5.
Answer:

Atomic number = 2 + 8 + 5

15 = no. of electrons.

Question 12. List any two properties of the element belonging to the first group of the modern periodic table.
Answer:

1. Elements are monovalent.
2. Elements are metal/electropositive.
3. Elements form basic oxides, (any two)

Question 13. Write two reasons responsible for the late discovery of noble gases.
Answer:

They are less available in nature.

They do not react, i.e., inert.

Question 14. What are the names of group 1 and group 17 elements?
Answer:

1. Group 1- Alkali metals
2. Group 17- Halogens.

Question 15. The atomic numbers of 3 elements A, B, and C are 12, 18, and 20 respectively. State and give a reason for which 2 elements will show similar properties.
Answer:

A and C, as they belong to the same group, as they have the same number of valence electrons.

Question 16. Predict the maximum number of valence electrons possible for elements in the first period of the periodic table.
Answer: 2 (in Helium)

Question 17. How many vertical columns are there in the modern periodic table, and what are they called?
Answer:

18 vertical columns are present and they are called groups.

Question 18. Give the number of elements in the 2nd and 5th periods in the modern periodic table.
Answer:

2nd period- 8 elements

5th period- 18 elements

Question 19. Write the formula that determines the maximum number of electrons that the shell of an atom can accommodate.
Answer:

2n², where W is some shells.

Question 20. Why was the system of classification of elements into triads not found suitable?
Answer:

Because all the elements discovered at that time could not be classified into triads.

Question 21. Which can gain electrons easily O or F?
Answer:

F can gain electrons more easily because it is smaller.

Question 22. Name any two pairs of elements that were adjusted by Newlands in the same slot.
Answer:

1. Cobalt and Nickel
2. Caesium and lanthanum

Question 23. Arrange the following metals in decreasing order of their atomic size. Ca, Mg, Be, Ba.
Answer:

Ba > Ca > Mg > Be

Question 24. What would be the nature of oxides formed by the elements on the right-hand side of the periodic table?
Answer: Acidic

Question 25. On what basis we can classify elements?
Answer: Similarity in properties.

Question 26. What was the earliest attempt to classify elements?
Answer: They were classified as metals and non-metals.

Question 27. What is a metalloid? Name any two of them.
Answer:  The element which shows some properties of both metals and non-metals is called a metalloid. Example: Silicon and Boron.

Question 28. Name any two elements which were discovered later after Mendeleev’s periodic table.
Answer:  Gallium and germanium

Question 29. Which is smaller, Carbon or Nitrogen?
Answer: Nitrogen

Question 30. What is the place of metalloids in the periodic table?
Answer: In the middle.

Question 31. What did Mendeleev use the criteria in creating his periodic table?
Answer: 

The criteria used by Mendeleev to create his periodic table was a Periodic Law, as stated below:  “The physical and chemical properties of elements are periodic functions of their atomic masses”.

Question 32.

1. Lithium, sodium, and potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
2. Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

Answer:

Yes, lithium, sodium, and potassium are similar because these contain one electron in their outermost shell. The atoms of helium and Neon have their outermost shell filled and are thus unreactive gases.

Question 33. In the Modern Periodic Table, which are the metals among the first ten elements?
Answer:  Li, and Be are metals.

Question 34. By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristics? Ga Ge As Se Be
Answer:

As elements on the left side of the periodic table are more metallic, therefore, Beryllium (Be) has the maximum metallic character as it is found on the extreme left side of the periodic table.

Question 35. Why K is more reactive than Li?
Answer: K has a larger atomic size, therefore it can lose electrons due to less force of attraction between the nucleus and electrons.

Question 36. Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev.
Answer: GeCl₄, GaCl₃.

Question 37. If an element is placed in group 14, what will be the formula and the nature of the bonding of its chloride?
Answer: XCl₄; Covalent bonding.

CBSE Class 10 Science Chapter 2 Acids And Bases And Salts Very Short Question And Answer

Question 1. Name an acid-base indicator prepared at home.
Answer: Beetroot extract.

Question 2. What is aqua regia?
Answer: It is a mixture of Cone HC1 and Cone. HN03 in the ratio of 3: 1.

Question 3. What will happen to blue litmus when it is added to soda water?
Answer: It changes to red.

Question 4. Which acid and base are used in the formation of the following salts?

1. CuSO₄
2. NaNO₃

Answer:

1. Cu(OH)₂ and H₂SO₄
2. NaOH and HNO₃

Question 5. What are antacids? Explain their role in providing relief from stomachache.
Answer:

1. Antacids are mild bases.
2. Antacids neutralize the effect of extra acid produced in the stomach during indigestion and thus provide relief.

Question 6. Define indicators. Name two natural indicators obtained from plants.
Answer: Indicators are substances which give different colours in acidic or basic solutions. Natural indicators from plants are litmus and Vanilla extract.

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Question 7. Make a distinction between metals and non-metals concerning the nature of their oxides.
Answer: Metal gives basic oxides and non-metal gives acidic oxides.

Question 8. What is the neutralisation reaction?
Answer: When the effect of base is nullified by an acid and vice versa, it is called a neutralisation reaction.

Question 9. How does the chloride of lime differ chemically from calcium chloride?
Answer: The chloride of lime is CaOCl2, while calcium chloride is CaCl₂.

Question 10. What is meant by water of crystallisation in a substance? Explain with an example.
Answer: Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt,

Example: CuSO₄.5H₂O

Question 11. How does the change occur in the pH values of milk when it changes to curd? Axis.
Answer: When milk changes to curd, it becomes acidic due to the formation of lactic acid, Thus its pH value decreases and becomes less than 6.

Question 12. Why does 1 M HCl solution have a higher concentration of H⁺ ions than 1 M CH₃COOH solution?
Answer: The HCl solution is a strong city and, therefore, ionises completely as compared to the CH₃ COOH solution which is a weak acid. Due to complete ionisation, it contains a high concentration of H⁺ ions.

Question 13. What are olfactory indicators? 
Answer:  The substances whose odour changes in acidic or basic media are called olfactory indicators.

Question 14. Which one of the following has the higher concentration of H+ ions? 1 M HCl or 1 M CH₃COOH?
Answer: 1 M HCl has a higher concentration of H⁺ ions, being a strong acid, it ionises completely to furnish H⁺ ions.

Question 15. What effect does an increase in the concentration of H⁺(aq) in a solution have on the pH of the solution?
Answer:

The pH of a solution decreases with the increase in the concentration of H⁺(aq). It is so because pH is the negative logarithmic value of H⁺(aq) a solution. More are the H⁺(aq) in a solution, more is the acidity, and less is the pH value of that solution.

Question 16. Why is HCl a stronger acid than acetic acid?
Answer: On dissociation, HCl yields larger (H⁺) hydrogen ions for the same concentration as compared to acetic acid. So it is stronger than acetic acid.

Question 17. Dry HCl gas does not change the colour of dry blue litmus. Give reasons.
Answer: H⁺ ions from HCl cannot ionise to give H⁺ ions in the absence of water. Acidic property like change in colour of litmus depends on the production of H⁺ ions, hence there is no colour change.

Question 18. How is the pH of a solution of an acid influenced when it is diluted?
Answer: On dilution, the concentration of hydrogen ions per unit volume decreases and hence pH of the solution increases. Since pH is the negative logarithmic value of the concentration of hydrogen ions.

Question 19. How will you test for the gas which is liberated when HCl acid reacts with an active metal?
Answer: When a burning candle is brought near the jar filled with hydrogen gas, it burns explosively with a pop sound.

Question 20. Which bases are called alkalies? Give an example of alkalies.
Answer:  Soluble bases are called alkalies,

Example: Sodium hydroxide (NaOH).

Question 21. Write a balanced chemical equation for the reaction between Sodium carbonate and hydrochloric acid indicating the physical state ofthe reactants and the products.
Answer:

Na₂CO₃(s) + 2HCl(aq) → 2NaCl(aq)+ CO₂(g) + H₂O(l)

Question 22. What is meant by pH and pH in pH?
Answer: p in pH stands for potenz and H is for hydrogen.

Question 23. Write the chemical name and chemical formula of washing soda.
Answer:

• Chemical name-Sodium carbonate
• Chemical formula-Na₂CO₃.10H₂O

Question 24. How is the concentration of hydronium ions (HO⁺) affected when a solution of an acid is diluted?
Answer:

When a given amount of acid is added to water, on diluting, the concentration of hydronium ions decreases because there are present a fixed amount of hydronium ions (H₃O⁺) per unit volume of the solution.

Question 25. How is the concentration of hydroxide ion (OH^–) affected when an excess base is dissolved in a solution of sodium hydroxide?
Answer: The concentration of hydroxide ions (OH^–) increases when the excess base (which also supplies OH^– ions) is dissolved in a solution of sodium hydroxide.

Question 26. You have two solutions, A and B. The pH of solution A is 6 and the pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of these is acidic and which one is basic?
Answer: Lower pH means higher H⁺ ion concentration. Thus, solution ‘A’ has more H⁺ ion concentration. Therefore, solution A is acidic as the pH is less than 7 and solution B is basic as the pH is more than 7.

Question 27. What effect does the concentration of H⁺(aq) ions have on the nature of the solution?
Answer: More the H⁺(aq) ion concentration, the higher the acidic character of the solution

Question 28. Do the basic solution also have H⁺(aq) ions? If yes, then why are these basic?
Answer: Basic solutions have H⁺(aq) ions. But they are lesser in number than OH^– ions. Excess of OH^–(aq) ions counts for the basic character of basic solutions.

Question 29. Under what soil condition do you think a farmer would treat the soil of his field with quicklime(calcium oxide) slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Answer: Plants grow well in the pH range 6-8. So when soil becomes acidic, a farmer will do it. his fields with weak bases like quick lime or slaked lime.

Question 30. What is the common name of the compound CaOCl₂?
Answer: The common name of the compound, CaOCl₂ is bleaching powder.

Question 31. Why does an aqueous solution of an acid conduct electricity?
Answer: An aqueous solution of an acid contains charged particles which are responsible for the conduction of electricity.

Question 32. Why does dry HCl gas not change the colour of the dry litmus paper?
Answer: Dry HCl gas does not generate H⁺ ions and does not act as acid. Hence, cannot change the colour of dry litmus paper.

Question 33. Name the substance which on treatment with chlorine yields bleaching powder.
Answer: Slaked lime [Ca(OH)₂] or lime water on treatment with chlorine gives bleaching pow

Question 34. Name the sodium compound which is used for softening hard water.
Answer:  Sodium carbonate is used for softening hard water.

Question 35. Why does distilled water not conduct electricity, whereas rain water does ?
Answer:  Rainwater contains ions of acids, so it conducts electricity, whereas there are no ions in distilled water.

Question 36. Why do acids not show acidic behaviour in the absence of water?
Answer:  Acids in water give hydronium ions, which are responsible for their acidic behaviour. But in the absence of water acids do not generate hydronium ions and thus do not show acidic behaviour.

Question 37. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
Answer: The pH of milk falls below 6 as it turns into curd due to the formation of lactic acid during this process.

Question 38. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Answer: Plaster of Paris is calcium sulphate hemihydrate (CaSO₄.i H₂O). On exposure to moisture absorbs moisture and becomes gypsum (CaSO₄.i H₂O which does not have the required setting property.

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

Question 1. What happens when copper reacts with zinc sulphate?
Answer: No reaction, because copper is less reactive than zinc.

Question 2. Write the composition of aqua-regia.
Answer: A mixture of conc. HCl and conc. HNO₃ is the ratio 3: 1.

Question 3. Give the reason why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer: Because copper is a better conductor of heat than steel.

Question 4. Name and write the symbol of a metal that exists in a liquid state.
Answer:  Mercury (Hg)

Question 5. What is the valency of silicon with atomic number 14?
Answer: 4

Question 6. A green layer is gradually formed on a copper plate left exposed to air for a week in a bathroom. What could this green substance be?
Answer: Due to the formation of basic copper carbonate.

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Question 7. Name the metal which has a very low melting point and can melt with the heat of your palm.
Answer: Gallium

Question 8. Arrange the following metals in the decreasing order of reactivity. Na, K, Cu, Ag
Answer: Na, K, Cu, Ag.

Question 9. Give the composition of the alloys-brass’ and ‘bronze’.
Answer:

Brass-Cu and Zn

Bronze-Cu and Tin

Question 10. An alloy has a low melting point and is, therefore, used for electrical fuse. Name the alloy and write its constituents.
Answer: Solder, Pb and Sn.

Question 11. What is the formula of rust?
Answer: Fe₂O₃.xH₂O

Question 12. Name one metal and a non-metal found in a liquid state at room temperature.
Answer: Metal-mercury and Non-metal-bromine

Question 13. Name two metals which react with dil. HNO₃ to evolve H₂ gas.
Answer: Magnesium (Mg) and manganese (Mn).

Question 14. Why oxides of highly reactive metals cannot be reduced by carbon?
Answer: This is because these metals have more affinity for oxygen than carbon.

Question 15. Name any one metal which reacts neither with cold water nor with hot water but reacts with heated steam to produce hydrogen gas.
Answer: Iron (Fe), aluminium (Al) and zinc (Zn) do not react either with cold or hot water. They react with steam to form metal oxide and hydrogen,

Example:

3Fe(s) + 4H₂O(g)→ Fe₃O₄(s) + 4H₂(g)

Question 16. Among the metals-sodium, calcium, aluminium, copper and magnesium, name the metal which reacts with water only on boiling.
Answer: Magnesium

Question 17. What is formed when sodium absorbs moisture from air? Give equation also.
Answer: It forms sodium hydroxide.

⇒ \(2 \mathrm{Na}+2 \mathrm{H}_2 \mathrm{O} \longrightarrow 2 \mathrm{NaOH}+\mathrm{H}_2\)

Question 18. Why the sulphide and carbonate ores are converted into oxides?
Answer: It is because it is easier to obtain a metal from its oxide, as compared to its sulphide and carbonates.

Question 19. Why do we use copper and aluminium wire for the transmission of electric current?
Answer: Because they are a good conductor of heat and electricity.

Question 20. Name two metals which have very low melting points.
Answer:

1. Caesium
2. Gallium

Question 21. Name a non-metal which is lustrous and a metal which a non-lustrous.
Answer: Iodine is a non-metal which is lustrous. Iron is a metal which is non-lustrous.

Question 22. Write the balanced chemical equation for the reaction: Aluminium when heated in air. Write the name of the product.
Answer:

⇒ \(4 \mathrm{Al}+3 \mathrm{O}_2 \longrightarrow \underset{\text { (Aluminium oxide) }}{2 \mathrm{Al}_2 \mathrm{O}_3}\)

Question 23. Why do ionic compounds not conduct electricity in the solid state?
Answer: The movement of ions in the solid state is not possible due to their rigid structure.

Question 24. 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:

X Carbon Y = Diamond Z = Graphite.

Question 25. Name a non-metal which is lustrous and a metal which is non-lustrous.
Answer: Iodine and Iron

Question 26. The way, metals like sodium, magnesium and iron react with air and water is an indication of their relative positions in the ‘reactivity series’. Is this statement true? Justify your answer with examples.
Answer: Yes. It is the most reactive. Sodium reacts with cold water, while magnesium reacts with hot water. Iron reacts only with steam.

Question 27.

1. X+YSO₄ → XSO₄+ Y
2. Y + XSO₄ → No reaction

Out of the two elements ‘X’ and ‘Y, which is more reactive and why?
Answer:

‘X’ is more reactive than ‘Y’ because it displaces ‘Y’ from its salt solution.

Question 28. When a metal X is treated with cold water, it gives a base Y with the molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y, and Z.
Answer: X’ is Sodium, Y is Sodium hydroxide, and ‘Z’ is H₂(g).

Question 29. What is an alloy? State the constituents of solder.
Answer:  An alloy is a homogeneous mixture of two or more two metals, which have nearly the same atomic size. Solder consists of lead and tin.

Question 30. What are amphoteric oxides? Choose the amphoteric oxides from among the following oxides:
Answer: Na₂O, ZnO, Al₂O₃, CO₂, H₂O

Question 31. What is 24-carat gold? How will you convert it into 18-carat gold?
Answer: 24-carat gold is pure gold. It is converted into 18-carat gold by adding 6 parts of Copper to 18 parts of gold, i.e., 75% Au and 25% Cu.

Question 32. Why should the metal sulphides and carbonates be converted to metal oxides in the process of extraction of metal from them?
Answer: It is easier to obtain metal from its oxide, as compared to its sulphides and carbonates.

Question 33. Generally, when metals are treated with mineral acids, hydrogen gas is liberated but when metals (except Mn and Mg), are treated with HNO₃, hydrogen is not liberated, why?
Answer:  HNO₃ is not only an acid, but it is also a strong oxidizing agent. It oxidizes the hydrogen formed into water, itself HNO₃ is reduced to NO₂ or N₂O.

Question 34. An element forms an oxide, Al₂O, which is acidic. Identify A as metal or non-metal.
Answer: Since an oxide of the element is acidic, therefore, I will be a non-metal.

Question 35. Give two examples of each of the metals that are good conductors and poor conductors of heat respectively.
Answer: Good conductors of heat-Silver, copper and aluminium Poor conductors of heat-Lead and mercury

Question 37. Name two metals which are found in nature in the free state.
Answer: Gold and Platinum

Question 36. Write two examples of each of the metals that are good conductors and poor conductors of heat respectively.
Answer: Good conductors of heat are copper and silver. Poor conductors of heat are lead and mercury.

Question 37. Name one metal and one non-metal that exist in a liquid state at room temperature. Also, name two metals having melting points less than 310 K (37°C).
Answer: Metal in the liquid state is mercury, and non-metal in the liquid state is bromine. Gallium (Ga) and Caesium (Cs) have melting points below 310 K.

Question 38. Name two metals which will displace hydrogen from dilute acids and two metals which will not.
Answer: Magnesium and zinc would displace hydrogen from dilute acids, whereas metals low in reactivity series like copper and silver will not displace hydrogen from dilute acids.

Question 39. State two ways to prevent the rusting of iron.
Answer: Rusting of iron can be prevented by painting, oiling, greasing, galvanising, chrome painting, anodising or making alloys.

Question 40. What type of oxides are formed when non-metals combine with oxygen?
Answer: Acidic oxides are formed when non-metals combine with oxygen.

Question 41. Why is sodium kept immersed in kerosene oil?
Answer: Sodium is kept immersed in kerosene oil as it reacts vigorously with air to catch fire.

Question 42. Which metals do not corrode easily?
Answer: Metals which are below in the activity series like gold, silver, and platinum do not corrode easily.

Question 43. A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution.  The bangles sparkled like new but their weight was reduced drastically. The lady was upset, but after a futile argument, the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
Answer: Aqua Regina mixture of concentrated hydrochloric acid and concentrated nitric acid. in the ratio of 3: 1, since it dissolves gold.

Question 44. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer: Iron (steel) reacts with hot water, but copper does not.

Question 45. What are the constituents of solder alloy? Which property of solder makes it suitable for welding electrical wires?
Answer: Solder is an alloy of lead (50%) and tin (50%). It has a lower melting point than lead, as well as tin. So it is suitable for welding electric wires.

CBSE Solutions For Class 10 Science

• 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