Solution - A solution is a homogeneous mixture of two or more pure substances which are chemically non-reacting, whose composition can be varied within certain limits. The component which is present in a large proportion in the solution is called solvent and the component present in relatively small proportion is called solute.Types of solutions : Depending upon the physical state of solvent, solutions can be divided into three main groups :(a) Gaseous solutions :(i) Solvent - gas, solute - gas. e.g., air (oxygen and nitrogen).(ii) Solvent - gas, solute - liquid. e.g., humidity in air.(iii) Solvent - gas, solute - solid. e.g., camphor in nitrogen.(b) Liquid solutions :(i) Solvent - liquid, solute - gas. e.g., aerated drinks.(ii) Solvent - liquid, solute - liquid. e.g., ethanol in water.(iii) Solvent - liquid, solute - solid. e.g., salt solution in water.(c) Solid solutions :(i) Solvent - solid, solute - gas. e.g., $H_2$ in palladium.(ii) Solvent - solid, solute - liquid. e.g., amalgam of Hg with Na.(iii) Solvent - solid, solute - solid. e.g., alloys.