1998 General Studies, all questions

UPSC Prelims 1998 · General Studies

Question 130: Science and Technology

Assertion (A): Sodium metal is stored under kerosene. Reason (R): Metallic sodium melts when exposed to air.

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 (c).

Sodium reacts quickly with oxygen and moisture in air, and violently with water, giving hydrogen, so it is stored under kerosene to keep air and water away. A is true. R is false: sodium does not melt on exposure to air. Its melting point is about 98 degrees C; it tarnishes and may burn, but does not melt at room temperature.

  • A. Sodium is kept under kerosene.
  • R. Sodium does not melt in air; it reacts with oxygen and moisture, which is why it is stored under kerosene.

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 poor explanation.
  • (c) Right: A is true; R is false because sodium does not melt in air.
  • (d) A is true, so this fails.

Explanation: written by UPSC Grade, not by UPSC.

Practise this paper timedPrevious question

Source: UPSC, Civil Services (Preliminary) Examination 1998, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.