How can we differentiate between salt solution and pure liquid ???? >_<

A pure liquid will contain same type of particles and the constituents will be present in a fixed ratio, such as water. It cannot be separated into its constituents by simple methods, water breaks into Hydrogen gas and Oxygen gas upon electrolysis.

However a salt solution is a mixture containing salt and water, in which salt can be present in any ratio. The salt solution can be separated into its constituent (salt and water) by simple evaporation.