A solution is a mixture of two or more substance; this consists of one or more minority substances, the solute(s), dispersed in a majority substance, present in large amounts, the solvent. In the vast majority of solutions, there are solution, and the solvent. It is a liquid (although solid solution is possible). The term mixture can also be used more generally to describe a system with more than one substance, under conditions that include approximately equal's amount, where no one substance can be considered the solvent. It is easiest to consider chemical species that have no charge (are not ions).
The mole fraction of any substances in a liquid system is the equivalent variable to the partial pressure of a species in a gas, as in each case increasing this variable causes an increase in the number of molecules of the species per unit volume. That means that activity of a liquid is related to its mole fraction. An ideal solution of a mixture of two or more liquids, A and B, is one in which the interactions between similar pairs of molecules, A and B or A and B in a solution are same as in magnitude to those between the dissimilar molecules A and B. A good example is benzene and toluene, which are molecules with same shapes and sizes and have very similar interactions. In this case Raoult's law is obeyed, which is:
Raoult's law only applies to a very few systems at all compositions. It is rare for the interactions between A and B to be exactly the same. That greatly complicates the situation for high concentrations of solute. For all solutions where the solute (B) is at a very low concentration. The entire surface consists of solvent the presence of molecules of B and molecules (A) affects only a small number of solvent molecules. In this case, the vast majority of A molecules interactions are with other A molecules, which means that Raoult's law applies to the solvent vapor. Solution under these conditions is called ideal solution. The chemical potential of the solvent in the liquid state is then given by