When intermolecular attraction between two components A and B in the mixture is same as between A and A or B and B, hence it is a case of ideal solution. When intermolecular attraction between A and B in a mixture is smaller than that between A and A or B and B, then mixture is more vaporised, bp is lowered. It is a case of positive deviation from Raoult’s law. When intermolecular attraction between A and B is higher than that between A and A or B and B, then mixture is less vaporised, bp is increased. It is a case of negative deviation.

(a) Methanol molecules (CH)₃OH are hydrogen bonded. In a mixture of CCl₄ and CH₃OH, extent of H-bonding is decreased. Mixture is more vaporised thus, positive deviation from Raoult’s law.

(b) Acetone molecules have higher intermolecular attraction due to dipole-dipole interaction. With CS₂ , this interaction is decreased thus, positive deviation.

(c) Mixture of benzene and toluene forms ideal solution.

(d) Phenol and aniline have higher interaction due to intermolecular H-bonding. Hence, negative deviation.