How does a chemist count the number of particles in a given number of moles of a substance?

The chemist the count the number of particles (Atoms, Molecules or Formula Unit) in a given number of moles of a substance by using following relationship.

                              Moles  =  # of Particles / 6.022 × 10²³

Or,

                              # of Particles  =  Moles × 6.022 × 10²³

So, from above relation it is found that 1 mole of any substance contains exactly 6.022 × 10²³ particles. Greater the number of moles greater will be the number of particles.