A binary solution is a homogeneous mixture of two or more than two substances whose composition can change within a certain limits. The boiling point of binary solution depends upon the solution composition and there can be three cases:

1. the boiling points of solutions of all compositions lie between the boiling points of clean liquids
2. the boiling points of solutions of any composition lie above the boiling points of clean liquids
3. the boiling points of solutions of some compositions lie below the boiling points of clean liquids