UPSC Prelims 2006 · General Studies

Question 18: Geography

Assertion (A): To orbit around the Sun, the planet Mars takes lesser time than the time taken by the Earth. Reason (R): The diameter of the planet Mars is less than that of the Earth.

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 (d).

Mars is farther from the Sun than the Earth, so its orbit is longer and it moves more slowly: it takes about 687 Earth-days to go round the Sun, against the Earth's 365. The Assertion is therefore false. The Reason is true, as Mars's diameter is roughly half the Earth's. Orbital period depends on distance from the Sun (Kepler's third law), not on the planet's size.

A. Mars takes about 687 days, longer than the Earth's year.
R. Mars has roughly half the Earth's diameter.

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: Mars takes longer than the Earth.
(b) A is false, so it cannot be true with R.
(c) A is false, not true, and R is true, not false.
(d) Correct: A is false (Mars takes about 687 days) and R is true (Mars is smaller).

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2006, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.