Question

How is the vapour pressure of a solvent affected when a non-volatile solute is dissolved in it ?

Answer 1

When a non volatile solute is added to a solvent, the vapour pressure of the resulting solution is lower than the vapour pressure of pure solvent.
This is because, the surface area is partly occupied by non volatile solute molecules and partly by solvent molecules. Due to this, the rate of evaporation is lowered.