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Assertion (A): The amount of… (Class 10 Science 2025, Q20)

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ScienceCBSE Class 10 · Board exam 2025, set 31/1/1 · 1 mark · Assertion-reason

CBSE Class 10 Science 2025: question 20

Set in the CBSE Class 10 board exam of 2025, paper 31/1/1, section A, question 20, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q20 · 1 mark · Assertion-reasonCompetency-basedOur Environment

Assertion (A): The amount of ozone in the atmosphere began to drop sharply in the 1980s.
Reason (R): The oxygen atoms combine with molecular oxygen to form ozone.

  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.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/1/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

What caused ozone depletion?

Hint 2

Does a statement about ozone formation explain its depletion?

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. Ozone levels fell sharply in the 1980s, mainly because of CFCs. The Assertion is true.

  2. is how ozone forms, so the Reason is true.

  3. The Reason describes how ozone forms, not why it decreased. The answer is option (B).

    1 mark

Answer: Option (B)

Where the marks are

  • Chooses option (B) (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Our Environment, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 31/1/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.