1 mole is the amount of substance that contains as many particles as there are atoms in exactly 12 g of ¹²C isotope.

As mass of 1 atom of carbon is 1.9926 x 10^-23 g and 1 mole of carbon weights 12 g.

The no. of atoms in 12g of carbon is = 12 / 1.9926 x 10^-23 = 6.022 x 10²³ atoms / mol.

This no. is given a name = Avogadro’s constant

Or Avogadro’s no. its represented as no. Avogadro no. may be defined as the no. of atoms.

Present in 1g atom of element or no. of molecules in 1g molecule of substance.

1 mole = 1 gram atom = 6.022 x 10²³ atoms = atomic mass

Mole of a gas at STP is = 22.4 litre volume.

No. of moles = mass of substance / moles or atomic mass.

Empirical formula:-  it is defined as the simplest whole number ratio of atoms in a compound.

Molecular formula:- it represents the actual number of atoms in a given compound.

eg. Molecular formula of benzene is C6H6 and empirical formula of benzene CH and the ratio is 6 : 1