Which has the greater number of atoms: 4g of Na, 4g of He, 4g of Ne (Chemistry a level - moles)?

Mass of each element = 4 g

No. of moles = Mass / Molar mass
No. of moles = 4.0 g / Molar mass
Obviously, the smaller the molar mass of the atom, the greater number of atoms is.

Molar mass: He (4.0 g/mol) < Ne (20.2 g/mol) < Na (23.0 g/mol)
Hence, no. of atoms: He > Ne > Na

Ans: He has the greatest number of atoms.