How many atoms are in 4.00 moles of helium?

Avogadro's number represents the number of units in one mole of any substance. This has the value of 6.022 x 10^23 units / mole. This number can be used to convert the number of atoms or molecules into number of moles.

4 mol He (6.022 x 10^23 atoms / mole) = 2.4088 x 10^34 atoms He