PLEASE SPECIFY THE QUESTION whether it is elements , molecule or even the certain volume of gas .
here is the calculation of no of atoms in element .
You can use Avogadro calculation:
1 mole =6.02×10^23particle
Every element have unique atomic mass (or atomic weight). If you want to calculate the number of atoms, first you need to measure mass of the element….
…. and then divide it by atomic mass, so you’ll get value of element in mole
.… then you just need to multiplying by Avogadro’s number 6.02×10^23 so you’ll get number of atoms.