Non-ideal solution is the one which does not obey theRaoult'slaw. The mixture has a minimum boiling point that means it has a maximum vapour pressure. Since the molecules are having a high VP means they have a tendency to escape more easily. Such a mixture cannot be separated completely by fractional distillation. We can only get either one of the components in pure state,not both.This can be deciphered on the basis of liquid-vapour equilibrium diagrams. This mixture of A-B shows positive deviation from Raoult's law.Suppose the mixture A-B has a composition x. The vapour given off has composition x1. So, the composition of distillate will shift towards C and residue towards A.so by repeated distillation we will only be able to get pure A not B,in the end A and C are obtained. If the mixture has composition y then we get pure B and distillate C.On mixing the two there is enthalpy change and heat is absorbed , H=+ve.That means temperature gets lowered.