Question

Why is the vapour pressure of an aqueous solution of glucose lower than that of water

Answer 1

The vapour pressure of an aqueous solution of glucose lower than that of water.
It is because in glucose solution, the surface of liquid consists of both solute and solvent molecules, therefore, the fraction of surface covered by the solvent molecules gets reduced.
Hence, escaping tendency of solvent molecules into vapours also gets reduced, thus, vapour pressure of glucose solution decreases.