Class 10 Science · Chapter 13

Our Environment

141 Class 10 Science questions on Our Environment from the NCERT textbook, NCERT Exemplar and CBSE board papers 2024–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 4 of 8

1. Q61 CBSE 2026
   Decomposers ​play ​an ​important role in the nature. ​Which role ​do ​they not perform ?

   1. (a)Convert simple inorganic substances into complex organic substances using radiant energy of the Sun.
   2. (b)Act on the garbage and reduce it.
   3. (c)Natural replenishment of the soil.
   4. (d)Breakdown of complex organic matter of dead animals and plants into simple form.
   Show answer

   (a) Convert simple inorganic substances into complex organic substances using radiant energy of the Sun.

   Step-by-step solution →
2. Q62 CBSE 2026
   In ​terms ​of various trophic levels of ​a food ​chain, which of the following organisms belong to ​the same level ?

   1. (a)Snake and Grasshopper
   2. (b)Grass and tree
   3. (c)Lizard and elephant
   4. (d)Bacteria and grass
   Show answer

   (b) Grass and tree

   Step-by-step solution →
3. Q63 CBSE 2026
   In ​the ​given figure, identify the ​trophic level ​having ​maximum concentration of harmful ​chemicals.

   1. (a)T1
   2. (b)T5
   3. (c)T4
   4. (d)T3
   Show answer

   (b) T5

   Step-by-step solution →
4. Q64 CBSE 2026
   In ​accumulation of toxic substances ​at ​higher trophic levels of ​an ecosystem through the food ​chain, ​which of the ​following organisms ​is affected the most ?

   1. (a)Small aquatic plants
   2. (b)Human beings
   3. (c)Small fish
   4. (d)Large fish
   Show answer

   (b) Human beings

   Step-by-step solution →
5. Q65 CBSE 2026
   Which ​of ​the ​following ​is a ​non-biodegradable pollutant ​?

   1. (a)Paper
   2. (b)DDT
   3. (c)Wood
   4. (d)Vegetable peel
   Show answer

   (b) DDT

   Step-by-step solution →
6. Q66 CBSE 2026
   In a food chain, ​where plants ​are eaten by insects, ​insects are ​eaten by frog and frog is ​eaten by snake, if the energy available to the frog is $100$ J, ​then the energy available to the ​insects and snake respectively will be :

   1. (a)$1000$ J and $10$ J
   2. (b)$10000$ J and $10$ J
   3. (c)$10$ J and $1000$ J
   4. (d)$1000$ J and $100$ J
   Show answer

   (a) $1000$ J and $10$ J

   Step-by-step solution →
7. Q67 CBSE 2026
   Which ​of ​the ​following ​group ​is ​not ​‘biodegradable’ ?

   1. (a)Vegetable peels, dead leaves, paper
   2. (b)Cow dung, leather bag, water
   3. (c)Polythene bag, rubber band, ball pen
   4. (d)Paper, fruits, bones
   Show answer

   (c) Polythene bag, rubber band, ball pen

   Step-by-step solution →
8. Q68 CBSE 2026
   Which ​of the following limits ​the number ​of trophic levels ​in a ​food ​chain ?

   1. (a)Availability of water
   2. (b)Deficient food supply
   3. (c)Decrease in energy at higher levels
   4. (d)Pollution in air
   Show answer

   (c) Decrease in energy at higher levels

   Step-by-step solution →
9. Q69 CBSE 2026
   In an ​ecosystem, the ​decomposers perform ​an important ​role. ​Select ​the option ​indicating the ​role of decomposers.

   1. (a)Convert inorganic materials to simpler forms
   2. (b)Break down complex organic substances to simple inorganic substances.
   3. (c)Break down inorganic substances into organic substances.
   4. (d)Do not act on organic compounds.
   Show answer

   (b) Break down complex organic substances to simple inorganic substances.

   Step-by-step solution →
10. Q70 CBSE 2026
    The reasons for excessive generation of ​wastes are :

    1. (i)Use and ​throw policy.
    2. (ii)Increased ​availability ​of packaged food.
    3. (iii)​Increased construction wastes.
    4. (iv)Non-sorting ​of dry ​and wet wastes. Options :

    1. (a)(i), (iii) and (iv)
    2. (b)(i), (ii) and (iii)
    3. (c)(i), (ii), (iii) and (iv)
    4. (d)(ii), (iii) and (iv)
    Show answer

    (c) (i), (ii), (iii) and (iv)

    Step-by-step solution →
11. Q71 CBSE 2026
    Consider the following statements about ​ozone and choose the correct option :

    1. (i)One ​molecule of ozone gas is formed by three atoms of oxygen.
    2. (ii)Ozone is the ​product of ​UV radiations acting on oxygen (${\text{O}}_2$) molecules.
    3. (iii)​Ozone performs an ​essential function at the lower levels of the atmosphere.
    4. (iv)Ozone is very useful and is ​essential for all ​aerobic forms of life. Options :

    1. (a)(i) and (iii)
    2. (b)(i) and (ii)
    3. (c)(ii) and (iv)
    4. (d)(iii) and (iv)
    Show answer

    (b) (i) and (ii)

    Step-by-step solution →
12. Q72 CBSE 2026
    For Questions number 8 and 9, ​two statements are given — one ​labelled as Assertion ​(A) and the other ​labelled as Reason (R). Select the correct answer to these ​questions ​from the ​codes ​(a), (b), (c) and (d) as given below.

    Assertion (A): Natural replenishment of soil will not take place in absence of microbes.

    Reason (R): Microbes, comprising of bacteria and fungi, break down dead remains and waste products of organisms, and they go into the soil.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).

    Step-by-step solution →
13. Q73 CBSE 2026
    This question consists of two ​statements ​— Assertion ​(A) and Reason (R). Answer ​the ​question by ​selecting the appropriate option from ​(a), (b), (c) and (d) given below :

    Assertion (A): Highest percentage of pesticides is found in tertiary consumers in a food chain.

    Reason (R): Chemicals / pesticides get accumulated progressively at each trophic level.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

    Step-by-step solution →
14. Q74 CBSE 2026
    Directions : Question ​numbers 8 and 9 are Assertion and Reason ​based questions. ​Two statements are given, one labelled as Assertion (A) ​and the other is labelled ​as Reason (R). Select ​the correct answer to these questions from ​the codes (a), (b), (c) ​and (d) as given below :

    Assertion (A): Ozone at higher levels of atmosphere is a product of UV radiation acting on oxygen molecule.

    Reason (R): The higher energy of UV splits apart some molecular ${\text{O}}_2$.

    1. (a)Both, Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both, Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (a) Both, Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

    Step-by-step solution →
15. Q75 CBSE 2026
    For Questions number 8 and 9, two statements ​are given — ​one ​labelled ​as Assertion (A) and the other labelled as Reason (R). ​Select the correct answer to these questions from the codes (a), (b), ​(c) and (d) as given below.

    Assertion (A): There are generally a greater number of individuals at the lower trophic levels of an ecosystem.

    Reason (R): The greatest number is of the producers.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

    Step-by-step solution →
16. Q76 CBSE 2026
    For Questions number 8 and ​9, two statements are ​given — one labelled ​as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these ​questions from ​the codes ​(a), (b), (c) ​and (d) as ​given below.

    Assertion (A): Ozone (${\text{O}}_3$) gas at higher levels of atmosphere is a product of UV radiation acting on Oxygen (${\text{O}}_2$).

    Reason (R): The amount of ozone in the atmosphere began to drop sharply in 1980s.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

    Step-by-step solution →
17. Q77 CBSE 2026
    Question No. 8 ​& ​9 ​consists of ​two statements – ​Assertion (A) and Reason (R). Answer these ​questions selecting the appropriate option from (a), (b), ​(c) and (d) given below ​:

    Assertion (A): The energy transferred to a lion when it eats a deer is only a small fraction of the deer’s total energy content.

    Reason (R): Energy transfer is efficient at all trophic levels with nearly 90% of energy passed on to the next level.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (c) Assertion (A) is true, but Reason (R) is false.

    Step-by-step solution →
18. Q78 CBSE 2026
    For Questions number 8 ​and 9, two statements are ​given — one labelled ​as Assertion ​(A) and the other labelled as Reason ​(R). Select the correct answer to these ​questions from the codes (a), (b), (c) and ​(d) as given below.

    Assertion (A): Oxygen at the higher levels of the atmosphere is a product of UV radiation.

    Reason (R): At higher levels of the atmosphere, ozone shields the surface of the Earth from UV radiation from the Sun.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (d) Assertion (A) is false, but Reason (R) is true.

    Step-by-step solution →
19. Q79 CBSE 2026
    For Questions ​number 8 ​and 9, ​two statements are given ​— one labelled as Assertion ​(A) and the other labelled as ​Reason (R). Select the ​correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): Biological magnification leads to the accumulation of maximum concentration of harmful chemicals in human beings.

    Reason (R): Human beings occupy the top level in any food chain.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).

    Step-by-step solution →
20. Q80 CBSE 2026
    What ​are ​decomposers ​? List two important roles they play ​in ​the ​environment.
    Show answer

    Decomposers are bacteria and fungi that break dead remains into simple substances; they replenish the soil and air and keep the environment clean.

    Decomposers are micro-organisms, mainly bacteria and fungi, that feed on the dead remains and waste products of plants and animals and break their complex organic compounds down into simple inorganic substances such as carbon dioxide, water, nitrates and minerals. Two important roles they play in the environment are: (i) They replenish the soil and the air. The nutrients locked inside dead bodies are released back into the soil and the atmosphere, where green plants absorb them and use them again, so the same stock of nutrients circulates indefinitely and the nitrogen, carbon and other biogeochemical cycles keep turning. (ii) They keep the environment clean. They dispose of the dead bodies, fallen leaves, dung and other organic wastes that would otherwise pile up on the surface of the earth, take up space and spread disease, which is also why they are put to work in compost pits and sewage treatment plants.

    Step-by-step solution →