1 mole is the amount of substance that contains the same number of entities as there are atoms in exactly 12 g of the 12 C isotope.
∴ Number of atoms in 12 g of 12C-isotope
= 6.023 × 1023 atoms/mol
The term ‘mole’ is given by the “Amedeo Avaogadro”. So it is also known as Avogadro’s number (NA).
∴ 1 mole =NA= 6.023 × 1023 atoms, molecules, ions etc.