UPSC Prelims 2013·CSAT·Reading Comprehension·Passage Comprehension

Passage Crude mineral oil comes out of the earth as a thick brown or black liquid with a strong smell. It is a complex mixture of many different substances, each with its own individual qualities. Most of them are combinations of hydrogen and carbon in varying proportions. Such hydrocarbons are also found in other forms such as bitumen, asphalt and natural gas. Mineral oil originates from the carcasses of tiny animals and from plants that live in the sea. Over millions of years, these dead creatures form large deposits under the sea-bed; and ocean currents cover them with a blanket of sand and silt. As this mineral hardens, it becomes sedimentary rock and effectively shuts out the oxygen, so preventing the complete decomposition of the marine deposits underneath. The layers of sedimentary rock become thicker and heavier. Their pressure produces heat, which transforms the tiny carcasses into crude oil in a process that is still going on today. Sedimentary rock leads to the formation of oil deposits because

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Last updated 23 May 2026, 3:31 pm IST
  1. Athere are no saline conditions below it
  2. Bit allows some dissolved oxygen to enter the dead organic matter below it
  3. Cweight of overlying sediment layers causes the production of heatCorrect
  4. Dit contains the substances that catalyze the chemical reactions required to change dead organisms into oil.

Explanation

The passage states, "The layers of sedimentary rock become thicker and heavier. Their pressure produces heat, which transforms the tiny carcasses into crude oil..." This directly supports option C, as the weight of the overlying sediment layers (sedimentary rock) creates pressure that produces heat, leading to oil formation. Option A is incorrect because the oil originates from marine life, implying saline conditions. The passage does not mention the absence of saline conditions as a factor. Option B is incorrect because the passage explicitly states that sedimentary rock "effectively shuts out the oxygen, so preventing the complete decomposition." Allowing oxygen would hinder oil formation. Option D is incorrect because the passage attributes the transformation to "pressure produces heat," not to catalysts contained within the sedimentary rock.
Reading Comprehension: Passage Crude mineral oil comes out of the earth as a thick brown or black liquid with a strong smell. It is a complex m
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