Note: Positive deviations are shown by such solutions in which solvent-solvent and solute-solute interactions are stronger than the solvent-solute interactions. In such solutions, the interactions among molecules becomes weaker. Therefore, their escapingtendency increases which results in the increase in their partial vapour pressure. In a solution of methanol there exists intermolecular H-bonding.
In this solution benzene molecules come between methanol molecules which weaken intermolecular forces. This results in increase in vapour pressure.