UPSC Prelims 2001 · General Studies

Question 103: Science and Technology

Assertion (A): The boiling point of water decreases as the altitude increases. Reason (R): The atmospheric pressure increases with altitude.

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

bBoth A and R are individually 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 (c).

A is true: water boils when its vapour pressure equals the surrounding air pressure, and the air pressure is lower at altitude, so the boiling point falls. R is false, since atmospheric pressure decreases, not increases, with altitude. Remember that this is why cooking takes longer in the hills and why a pressure cooker helps.

A. The boiling point of water falls with altitude.
R. Atmospheric pressure falls with altitude.

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) R is false, so it cannot explain A.
(b) R is false, not merely a non-explanation.
(c) Right: A is true, R is false.
(d) A is true, not false.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2001, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.