UPSC Prelims 2021— Question 75

Magnetite nanoparticles can arise from combustion and high-temperature processes and have been associated with traffic-related sources, including brake wear and engine emissions, as well as industrial sources such as power generation. Microwave ovens and telephone lines are not established environmental sources in this context. Hence the accepted combination is 1, 2 and 4. The final answer-key position for Set C identifies option B as the correct option. Option A — 1, 2, 3 and 5 only — is not correct because it does not satisfy the specific condition tested in the question; it represents an alternative that is contradicted, incomplete, or less precise than the accepted answer. Option B — 1, 2 and 4 only — is correct because it is the alternative that matches the constitutional, historical, geographical, scientific or economic principle established above. Option C — 3, 4 and 5 only — is not correct because it does not satisfy the specific condition tested in the question; it represents an alternative that is contradicted, incomplete, or less precise than the accepted answer. Option D — 1, 2, 3, 4 and 5 — is not correct because it does not satisfy the specific condition tested in the question; it represents an alternative that is contradicted, incomplete, or less precise than the accepted answer. For PYQ interpretation, the distinction between the correct alternative and merely related facts is important. UPSC often places plausible distractors beside the precise statement that matches the underlying rule, chronology, definition or empirical relationship. The answer should therefore be read against the exact wording of the question rather than against a broadly related fact.