UPSC Prelims 2023— Question 20

This question tests Hydrofluorocarbons under Ozone & Greenhouse Gases. The central point is HFCs have applications in aerosols, foams and fire suppression, not lubricants. Option A: Only one. This distractor is not the keyed answer because it conflicts with the specific factual relationship, chronology, institutional role, geographic association or conceptual distinction tested in the question. Option B: Only two. This distractor is not the keyed answer because it conflicts with the specific factual relationship, chronology, institutional role, geographic association or conceptual distinction tested in the question. Option C: Only three. This is the keyed answer because it matches the governing fact or concept: HFCs have applications in aerosols, foams and fire suppression, not lubricants. Option D: All four. This distractor is not the keyed answer because it conflicts with the specific factual relationship, chronology, institutional role, geographic association or conceptual distinction tested in the question. The question should be approached by checking each statement independently rather than accepting a familiar phrase at face value. This is particularly important in UPSC questions where a single incorrect institutional attribution, location, chronology, absolute word or causal link can invalidate an otherwise plausible option. The broader revision takeaway is to connect the keyed answer with the underlying concept rather than memorizing only the letter. The options also illustrate how UPSC constructs distractors by mixing correct facts with one altered detail. In revision, candidates should therefore retain both the positive fact and the nearest contrasting fact so that the same concept can be recognized when the framing changes in another year.