UPSC Prelims 2003 · General Studies

Question 105: Science and Technology

Assertion (A): In the periodic table of chemical elements, electron affinity is always found to increase from top to bottom in a group. Reason (R): In a group, the atomic radius generally increases from top to bottom.

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 the correct explanation of A

cA is true but R is false

dA is false but R is true

AnswerThe answer is (d).

Electron affinity does not always increase down a group; in general it decreases down a group because the added electron goes into a larger, more distant shell, with exceptions such as fluorine, whose small size makes its affinity lower than chlorine's. So A is false. R is true: atomic radius increases down a group as more shells are added.

A. Electron affinity generally decreases down a group, with exceptions.
R. Atomic radius increases down a group as shells are added.

How you could have got this

If you were sure statement 1 is not correct, only (d) is left: every other option says it is correct.

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) A is false, so both cannot be true.
(b) A is false, so 'both true, R not the explanation' fails.
(c) A is false, so 'A true, R false' fails.
(d) Correct: A is false and R is true.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2003, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.