Avogadro‟s law states that “equal volumes of all gases under the same conditions of temperature and pressure contain equal number of molecules”. Or

Avogadro‟s law can also be stated as “the volume of a gas is directly proportional to its number of moles as long as the temperature and pressure are kept constant”.

Mathematically, Vα n at constant P & T or V = kn at constant P& T.