The binary mixture of a particular composition in both liquid and vapour state is known as a/an azeotropic mixture. Such a mixture corresponds to a maximum or minimum in the vapour pressure curve.At this point, the liquid and vapour curves are tangent to each other. Hence, the liquid and the vapour has the same composition. When an azeotropic mixture is distilled, the vapour and the distillate has the same composition as the original azeotropic mixture. Hence, no separation is achieved.