Question

Assertion (A) When non-volatile solute is added to solvent, the vapour pressure of the solution decreases.
Reason (R) As number of solvent molecules escaping from the surface is reduced, the vapour pressure of the solution is also reduced.

• A. Both $A$ and $R$ are correct, $R$ is the correct explanation of $A$.
• B. Both $A$ and $R$ are correct, $R$ is not the correct explanation of $A$.
• C. $A$ is correct, $R$ is incorrect.
• D. $A$ is incorrect, $R$ is correct.

Answer 1

Answer: (A)

In solution, the surface has both solute and solvent molecules, thereby the fraction of the surface covered by the solvent molecules get reduced. Consequently, the number of solvent molecules escaping from the surface is reduced, thus vapour pressure of the solution is also reduced.