The partial vapour pressure of an electrolyte at the following concentrations, decreases in the order

(A) 0.5 M
(B) 0.1 M
(C) 0.05 M
(D) 0.001 M

Choose the correct answer from the options given below:

(A), (B), (C), (D)

The correct answer is Option (1) → (A), (B), (C), (D)

Note: The given answer i.e. Option 1 ( (A), (B), (C), (D)) is marked as per NTA answer key. However, there is a mistake in the NTA answer. The correct answer should be Option 4 -(D), (C), (B), (A) as explained below.

The partial vapour pressure decreases as concentration increases.

Reasoning:
For an electrolyte solution, vapour pressure lowering is a colligative property.
Higher concentration → more solute particles → greater lowering of vapour pressure → smaller vapour pressure value.

So the solution with highest concentration has the lowest vapour pressure.

Order of concentrations from highest to lowest:
0.5 M > 0.1 M > 0.05 M > 0.001 M

Hence, the order of decreasing vapour pressure (largest to smallest reduction / highest to lowest vapour pressure drop) is:

(D) 0.001 M > (C) 0.05 M> (B) 0.1 M > (A) 0.5 M