The cause for deviation from Raoult’s law in the colligative properties of non-ideal solutions lies in the nature of interactions at the molecular level. These properties show deviations from Raoult’s law due to difference in interactions between solute–solvent, solute–solute and solvent–solvent. Some liquids on mixing form azeotropes which are binary mixtures having the same composition in liquid and vapour phase and boil at a constant temperature. In such cases, it is not possible to separate the components by fractional distillation. There are two types of azeotropes called minimum boiling azeotrope and maximum boiling azeotrope. (a) Pure ethanol cannot be prepared by fractional distillation of ethanol–water mixture. Comment.