Joankessler parkland

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