Calculate the number of atoms in each of the following (i) 52 moles of Ar (ii) 52 u of He (iii) 52 g of He.

(i) 1 mole of Ar = 6.022 × 10²³ atoms of Ar

52 mol of Ar = 52 × 6.022 × 10²³ atoms of Ar

= 3.131 × 10²⁵ atoms of Ar

(ii) 1 atom of He = 4 u of He

Or,

4 u of He = 1 atom of He

1 u of He atom of He

52u of He atom of He

= 13 atoms of He

(iii) 4 g of He = 6.022 × 10²³ atoms of He

52 g of He atoms of He

= 7.8286 × 10²⁴ atoms of He