Mole is defined as the amount of a substance, which contains the same number of chemical units (atoms, molecules, ions or electrons) as there are atoms in exactly 12 grams of pure carbon-12.
A mole represents a collection of 6.022 x1023( Avogadro's number) chemical units. The mass of one mole of a substance in grams is called its molar mass.
Molar Volume: The volume occupied by one mole of any substance is called its molar volume. It is denoted by Vm. One mole of all gaseous substances at 273 K and 1 atm pressure occupies a volume equal to 22.4 litres or 22,400 mL. The unit of molar volume is litre per mol or millilitre per mol.