Calculate the number of He atoms in (i) 52 u, (ii) 52 g, (iii) 52 moles of He. Atomic weight of He is 4u.

Explanation

(i) Atomic weight of Helium =4 i.e., 4 u is mass of 1 atom,
52 u is mass of `1/4 xx 52= 13` atoms.
(ii) 4 g of He contains `6.022 xx 10^(23)` He atoms /52 g of He contains?
`(6.022 xx 10^(23))/4 = 7.8286 xx 10^(23)` atoms.
(iii) 1 mole of He contains `6.022 xx 10^(23)` atoms, 52 moles of He contains
`52 xx 6.022 xx 10^(23) = 3.131 xx 10^(25)` atoms.