Why is the vapour pressure of an aqueous solution of glucose lower than that of water?
In pure liquid, the entire surface of liquid is occupled by the molucules of water. When a non-volatile solute, e.g., glucose is dissolved in water, the fraction of surface covered by the solvent molecules gets reduced because some positions are occupied by glucose molecules.
So, number of solvent olecules escaping from the surface is reduced. That is why vapour pressure of aqueous solution of glucose is reduced.