UPSC Prelims 2021— Question 34

Black cotton soil, or regur soil, is closely associated with basaltic Deccan Trap rocks. These are dark, fine-textured, clay-rich soils formed largely from weathering of fissure-erupted basalt. Brown forest soils, granite and schist, or shale and limestone are not the principal parent materials associated with India's classic black cotton soil. Hence fissure volcanic rock is correct. The final answer-key position for Set C identifies option B as the correct option. Option A — brown forest soil — 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 — fissure volcanic rock — is correct because it is the alternative that matches the constitutional, historical, geographical, scientific or economic principle established above. Option C — granite and schist — 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 — shale and limestone — 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.