How many moles are in 12.013 x 10 ^24 atoms of helium?

19.948 mol.

Explanation:

Knowing that every one mole of a substance contains Avogadro's no. of molecules (NA = 6.022 x 10²³).

Using cross multiplication:

1.0 mole → 6.022 x 10²³ atoms of He.

? mole → 12.013 x 10²⁴ atoms of He.

∴ The no. of moles of are in 12.013 x 10²⁴ atoms of He = (12.013 x 10²⁴ atoms of He) (1.0 mole) / (6.022 x 10²³ atoms of He) = 19.948 mol.