Question

Which one of the statements given below concerning properties of solutions describes a colligative effect?

• A. Boiling point of pure water decreases by the addition of ethanol
• 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

Answer 1

The correct option is C Vapour pressure of pure benzene decreases by the addition of naphthalene

Option (C) is correct.Vapour pressure of pure benzene decreases by the addition of naphthalene.Naphthalene is non -volatile in nature so it decreases the vapour pressure of benzene.
Addition of a non-volatile solute always lowers the vapour pressure.