UPSC Prelims 2021— Question 71

Lemongrass is widely used in preparations for natural mosquito repellents because its essential oil contains compounds such as citronellal and citral that have insect-repellent properties. Congress grass is a major invasive weed, elephant grass is primarily a fodder grass, and nut grass has other traditional uses. The relevant plant for mosquito-repellent preparation is lemongrass. The final answer-key position for Set C identifies option C as the correct option. Option A — Congress grass — 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 — Elephant grass — 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 — Lemongrass — is correct because it is the alternative that matches the constitutional, historical, geographical, scientific or economic principle established above. Option D — Nut grass — 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.