Question
NEET 2022 (paraphrased): Regarding the ozone layer, which of the following statements is correct? (a) location refers to measure of ozone column thickness (b) Dobson units is characterised by stratosphere, 15–35 km above surface (c) CFCs — main culprit; Cl• catalytically destroys ozone (d) Montreal Protocol has no role in the ozone layer
Solution — Step by Step
This option swaps the definitions. location is actually stratosphere, 15–35 km above surface, not what (a) claims. So (a) is out.
Similarly, Dobson units means measure of ozone column thickness. Option (b) is mismatched. Out.
This one reads correctly: CFCs — main culprit; Cl• catalytically destroys ozone. Match with NCERT wording confirms it.
Montreal Protocol — 1987 treaty to phase out ozone-depleting substances — plays a real role in the ozone layer, so option (d) is factually wrong.
Correct answer: (c) CFCs — main culprit; Cl• catalytically destroys ozone.
Why This Works
NEET PYQs on the ozone layer rely on definition swapping. The examiner takes two correct facts and pairs them with the wrong terms. If you know each fact cold, the MCQ dissolves in 20 seconds.
Alternative Method
For definition-swap MCQs, don’t read all four options first. Read option (a), decide true/false, then (b), and so on. This prevents confusion between similar-looking options.
NEET reuses the same fact set every 2–3 years with different distractors. Master the four NCERT facts on the ozone layer listed here and you’ll handle almost any MCQ on this chapter.
Common Mistake
Students second-guess themselves when they see a familiar option listed as “wrong” in the stem. Trust the elimination — if you know the definition, stick with it.
Keep a one-page sheet of definitions for every NEET chapter. Revise only that sheet in the last 48 hours before the exam.