UPSC Prelims 2018— Question 81

**Concept and analysis:** Heavy sand mining from riverbeds can alter channel morphology, reduce groundwater recharge and disturb aquifers. It can therefore contribute to lowering of the groundwater table and groundwater-quality problems. The statement that it decreases river salinity is not a general consequence of riverbed sand mining. Hence the relevant consequences are pollution of groundwater and lowering of the water table. The question is testing precise UPSC-level identification rather than a broad association. The key is to distinguish the exact institutional, constitutional, historical, geographical, economic or scientific feature being asked. **Option-wise evaluation** **Option A:** Incorrect. It selects 1 only, but that combination does not match the verified statement-level assessment; it either includes a false statement or omits a true one. **Option B:** Correct. It selects statements 2, 3; these are the statements supported by the relevant constitutional, economic, historical, scientific or geographical facts. **Option C:** Incorrect. It selects 1 and 3 only, but that combination does not match the verified statement-level assessment; it either includes a false statement or omits a true one. **Option D:** Incorrect. It selects 1 ,2 and 3, but that combination does not match the verified statement-level assessment; it either includes a false statement or omits a true one. **UPSC takeaway:** The safest way to solve this type of question is to anchor the answer in the defining feature of the concept and then test every option against that feature. Closely related institutions or terms are often used as distractors. In statement-based questions, do not judge the option as a whole before checking each statement independently. In factual questions, compare the wording of each option with the exact definition, location, institutional role, chronology or scientific property. The correct answer follows from that verification rather than from familiarity with a keyword.