Calculate :
(i) The number of moles in 12 g. of oxygen gas. [O = 16]
(ii) The weight of 10^22 atoms of carbon.
[C = 12, Avogadro’s No. = 6 × 10^23]

(i) Gram molecular mass of oxygen = 32 g = 1 mole

32 g = 1 mole

∴ 12 g = 1\over32 × 12 = 0.375 moles.

(ii) 6 x 10²³ atoms of carbon weigh = 12 g

∴ 10²² atoms of carbon will weigh = 12 \over6 × 10^{23} × 10²²

= 0.2 g.

Hence, number of moles = 0.375 moles and weight of 10²² atoms of carbon = 0.2 g.