1)The relative number of particles(atoms, molecules, formula units)
2)The relative number of moles(very similar to the relative number of particle)
3)The relative volume of gases at constant temperature and pressure
Molar Volume- A vlume of 22.4 dm3 - the volume of 1 mole of a gas at STP
Avogadro's Hypothesis- Equal volumes of all gases under the same conditions of temperature and pressure contain the same number of molecules.