AIPMT 2010 Physics and Chemistry Paper

Vapour pressure depends upon the surface area of the solution. Larger the surface area, higher is the vapour pressure.
Addition of solute decreases the vapour pressure as some dites of the surface are occupied by solution particles, resulting in decreased surface area. However, addition of solvent, i.e., dilution, increases the surface area of the liquid surface, thus results in increased vapour pressure.
Hence, addition of water to the aqueous solution of (1 molal) KI, results in increased vapour pressure.