Q1. [1]
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.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Previously asked in CBSE board exam
2025 31/1/1 Q20
Generated by claude-sonnet-4-6 · 2026-06-15 06:42 · grounding rag
Model Answer
(B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A). The sharp drop in ozone was caused by CFCs, not by the natural ozone-formation process described in R.
Explanation
- A is true: The textbook explicitly states "The amount of ozone in the atmosphere began to drop sharply in the 1980s" due to CFCs.
- R is true: Oxygen atoms do combine with molecular oxygen (O + O₂ → O₃) — this is the natural ozone formation process, correctly stated.
- R does NOT explain A: Ozone formation and ozone depletion are opposite processes. The drop was caused by CFCs, not by ozone's natural formation mechanism. So option (B) is correct.
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