A mole of particles (atoms, ions or molecules) is defined as that amount of the substance which contains the same number of particles as there are present in 12 g of C-12 isotope.
Experimentally, it has been found that 0.012 kg of carbon-12 contains 6.022 x 10^23 atoms. This number is called Avogadro's number or Avogadro's constant and is represented by the symbol N0
Symbol of the unit of mole is mol.
Advantage of Mole Concept:
Any number of atoms and molecules can be selected conveniently, with the help of mole concept and its relation with the mass and volume of chemical substance.