Choose the right answer from following. Which one of the statements written below concerning properties of solutions, explain a colligative effect: (a) Boiling point of pure water decreases by the addition of ethano (b) Vapour pressure of pure water decreases by the addition of nitric acid (c) Vapour pressure of pure benzene decreases by the addition of naphthalene (d) Boiling point of pure benzene increases by the addition of toluene