UPSC Prelims 2000 · General Studies

Question 114: Science and Technology

Assertion (A): Large cold storage plants use ammonia as refrigerant while domestic refrigerators use chlorofluorocarbons. Reason (R): Ammonia can be liquified at ambient temperatures at low pressures.

aBoth A and R are true, and R is the correct explanation of A

bBoth A and R are true, but R is not a correct explanation of A

cA is true, but R is false

dA is false, but R is true

AnswerThe answer is (a).

Ammonia is cheap, efficient and easily liquefied at ordinary temperatures under moderate pressure, which suits large cold storages. It is toxic and irritating, so it is unsafe in homes, where leaks would harm people. Domestic refrigerators then used chlorofluorocarbons, which are non-toxic and non-flammable. So A is true, and R gives the reason ammonia suits large plants.

A. Large cold storages use ammonia, and domestic refrigerators then used chlorofluorocarbons.
R. Ammonia is easily liquefied at ambient temperature under moderate pressure, which explains its use in large plants.

How you could have got this

If you were sure statement 1 is correct, (d) goes. Then judge the second statement; if it is correct too, decide whether it explains the first.

This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.

Which options go is worked out from UPSC’s key and the options, not by a model.

Why each option is right or wrong

(a) Right: both are true, and R explains why large plants use ammonia.
(b) Treated here as wrong, since R does give the reason ammonia suits large plants.
(c) R is taken as true, so it cannot be called false.
(d) A is true, so it cannot be called false.

Worth knowing: Domestic refrigerators no longer use CFCs, which were phased out under the Montreal Protocol, so A is no longer true as stated.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2000, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.