With the help of suitable diagram show that lowering of vapour pressure of a solution than the pure solvent, causes a depression of freezing point for the solution compared to that of pure solvent.

 At freezing point, the vapour pressure of the solution equals the vapour pressure of the pure solid solvent .When a non-volatile solid is added to the solvent its vapour pressure decreases according to Roult’s law.The vapour pressure of the solution would become equal to that of solid solvent at lower temperature.Thus, the freezing point of the solvent decreases.