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.

Explanation

(i) 1 mole of Ar = `6.022 xx 10^(23)` atoms
`therefore 52` moles of Ar `=52 xx 6.022 xx 10^(23) = 3.131 xx 10^(25)` atoms of Ar.
(ii) 4u of He = 1 atom of He.
`therefore 52 u` of He `=52/4 = 13` atoms of He
(iii) 1 mole of He, i.e., 4 g of He contain `6.022 xx 10^(23)` atoms
`therefore` No. of He atoms in 52 g of `He = (6.022 xx 10^(23))/4 xx 52 = 7.8286 xx 10^(24)`