UPSC Prelims 2013 · CSAT

Question 32: Reading Comprehension

Passage beginning “Crude mineral oil comes out of the…” — Passage · as printed by UPSC

Mineral oil deposits under the sea do not get completely decomposed because they

aare constantly washed by the ocean currents.

bbecome rock and prevent oxygen from entering them.

ccontain a mixture of hydrogen and carbon.

dare carcasses of organisms lying in saline conditions.

AnswerUPSC’s answer is (b).

The passage describes dead sea creatures piling up under the sea-bed and being covered by sand and silt, which hardens into sedimentary rock. That rock shuts out oxygen, so the deposits below do not decompose completely. The reason is the oxygen-proof rock cover. Washing by currents, the hydrogen-carbon makeup of oil and saline conditions are not given as the reason. In a 'why' question, pick the mechanism the passage states, not a fact it merely mentions.

Why each option is right or wrong

(a) Wrong. Currents only cover the deposits with sand and silt; they do not protect them by washing.
(b) Right. The hardened rock keeps oxygen out, preventing complete decomposition.
(c) Wrong. Oil being a hydrogen-carbon mixture describes it, but does not explain why decomposition stops.
(d) Wrong. Their origin in carcasses is the source of oil, not the reason decomposition is incomplete.

Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.

Practise this paper timedPrevious question Next question

Source: UPSC, Civil Services (Preliminary) Examination 2013, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.