UPSC Prelims 1998 · General Studies

Question 102: Environment and Ecology

The water pollution in river is measured by the dissolved amount of

aChlorine

bOzone

cNitrogen

dOxygen

AnswerThe answer is (d).

Pollution of a river by organic waste is measured by the dissolved oxygen (DO) left in the water, and by biochemical oxygen demand (BOD), the oxygen microbes need to break the waste down. The more the pollution, the lower the DO, which fish and other aquatic life need to survive. Chlorine, ozone and nitrogen are not the standard measures.

Why each option is right or wrong

(a) Chlorine is used to disinfect water, not to measure its pollution.
(b) Ozone is a gas used in water treatment, not a measure of pollution.
(c) Nitrogen is not the standard measure of water pollution.
(d) Right: dissolved oxygen measures the pollution of water.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 1998, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.