Civil Services Prep

Prelims 2014 · Science and Technology · Question 50

Which of the following is/are the example/examples of chemical change? 1. Crystallization of sodium chloride 2. Melting of ice 3. Souring of milk. Select the correct answer using the code given below.

  1. 1 and 2 only
  2. 3 only
  3. 1, 2 and 3
  4. None

Answer

3 only

  1. Crystallization of sodium chloride — This is a physical change; only the form/state of NaCl changes, no new substance is formed. Verdict: Incorrect.

  2. Melting of ice — This is a physical change; ice and water are the same substance (H2O), and the change is reversible. Verdict: Incorrect.

  3. Souring of milk — This is a chemical change; lactic acid is formed by bacterial action, producing new substances. Verdict: Correct.

Hence, only 3 is an example of chemical change. Answer: (b).

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