Example (1) Calculate the no. of carbon dioxide molecules in
3moles of carbon dioxide CO2(C=12,0=16)
Solution:-

Number of molecules : 1.806 x 10²⁴

A mole is a number of particles(atoms, molecules, ions)  in a substance

This refers to the atomic total of the 12 gr C-12  which is equal to 6.02.10²³, so 1 mole = 6.02.10²³ particles  

Can be formulated :

N = n x No

N = number of particles

n = mol

No = 6.02.10²³ = Avogadro's number

3 mol CO₂ :

molecules ⇒