2014 GS Paper I, all questions

UPSC Prelims 2014 · GS Paper I

Question 70: Science and Technology

Which of the following is/are the example/examples of chemical change?

  1. 1.Crystallization of sodium chloride
  2. 2.Melting of ice
  3. 3.Souring of milk

Select the correct answer using the code given below.

a1 and 2 only
b3 only
c1, 2 and 3
dNone

AnswerUPSC’s answer is (b).

A chemical change forms a new substance that cannot easily be reversed. Milk turns sour because bacteria convert lactose into lactic acid, so souring is a chemical change. Crystallization of sodium chloride from solution is only a change of state of the same salt, and melting of ice is a change of state of water; both are physical changes. So only 3 is correct.

  • 1. Crystallizing salt only recovers the same substance.
  • 2. Melting of ice only changes the state of water.
  • 3. Bacteria turn lactose into lactic acid, a new substance.
Why each option is right or wrong
  • (a) Wrong. Both crystallization and melting are physical changes.
  • (b) Right. Souring of milk forms lactic acid and is a chemical change.
  • (c) Wrong. Statements 1 and 2 are physical changes.
  • (d) Wrong. Souring of milk is a chemical change.

Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.

Practise this paper timedPrevious questionNext question

Source: UPSC, Civil Services (Preliminary) Examination 2014, General Studies Paper I, Series A. The paper on upsc.gov.in.