UPSC Prelims 2021— Question 22

Conventional sodium street lamps are relatively directional systems whose familiar low-pressure sodium output is close to monochromatic yellow light; LED systems can provide more controlled directionality and a broader spectrum with better colour rendering. Sodium lamps are not characterized by a longer useful life than LEDs in the sense asserted. Hence statements 1 and 3 form the accepted combination. The final answer-key position for Set C identifies option C as the correct option. Option A — 3 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 — 2 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 C — 1 and 3 only — is correct because it is the alternative that matches the constitutional, historical, geographical, scientific or economic principle established above. Option D — 1, 2 and 3 — 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.