UPSC Prelims 2002 · General Studies

Question 150: Science and Technology

Assertion (A): An iron ball floats on mercury but gets immersed in water. Reason (R): The specific gravity of iron is more than that of mercury.

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).

Assertion A is true: iron, with a density of about 7.9 g/cm3, is lighter than mercury (13.6 g/cm3) so an iron ball floats on mercury, but it is denser than water and sinks in it. Reason R is false: the specific gravity of iron is less than that of mercury, not more. So A is true and R is false.

A. Iron floats on mercury and sinks in water.
R. Iron's specific gravity is lower than mercury's.

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, so this option fails.
(c) Right: A is true and R is false.
(d) A is true, so this option fails.

Explanation: written by UPSC Grade, not by UPSC.

Practise this paper timedPrevious question

Source: UPSC, Civil Services (Preliminary) Examination 2002, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.