Question

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

Assertion
When NaCl is added to water, a depression in freezing point is observed.
When NaCl is added to water, a depression in freezing point is observed.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect

Answer 1

NaCl added to water causes a depression in the freezing point, which is due to the lowering of the vapor pressure of the solution. This explanation is accurate, thus option A is correct, as both the assertion and reason are correct and the reason is the correct explanation for the assertion.

Step-by-step explanation:

The assertion that NaCl added to water causes a depression in the freezing point is correct. This is because the addition of solute to a solvent will lower the freezing point of the solution, a phenomenon known as freezing point depression.

However, the reason given in the student's question—"The lowering of vapor pressure of a solution causes depression in the freezing point."—is indeed the correct explanation for the assertion. When a nonvolatile solute, like NaCl, is dissolved in water, the vapor pressure of the solution decreases.

This reduced vapor pressure means that the freezing point of the solution is also decreased because the solid-liquid equilibrium is reached at a lower temperature when compared to the pure solvent.