The question given below consist of an assertion and a reason. Use the following key to choose the appropriate answer.

(a) Both Assertion and reason are correct statements, and Reason is the correct explanation of assertion.

(b) Both Assertion and reason are correct statements, and Reason is not the correct explanation of assertion.

(c) Assertion is correct, Reason is the wrong statement.

(d) Assertion is wrong, but Reason is the correct statement.

Assertion: When NaCl is added to water a depression in freezing point is observed.

Reason: The lowering in vapour pressure of a solution causes depression in freezing point. 

(a)

According to Raoult’s law, when a non-volatile solid is added to the solvent its vapour pressure decreases and now it would become equal to that of solid solvent at lower temperature. Thus, the freezing point of the solvent decreases.