Calculate :

(i) The number of moles in 12 g. of oxygen gas. [O = 16]

(ii) The weight of 10²² atoms of carbon.

[C = 12, Avogadro's No. = 6 x 10²³]

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

32 g = 1 mole

∴ 12 g = $\dfrac{1}{32}$ x 12 = 0.375 moles.

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

∴ 10²² atoms of carbon will weigh = $\dfrac{12}{ 6\times 10^{23}}$ x 10²² = 0.2 g.

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