Gay Lussac's Law — Avogadro's Law — Mole Concept — Question 12

Gram molecules is the relative molecular mass of a substance expressed in grams.

Relative molecular mass of N₂ = 2 x 14 = 28 g

$\text{Gram molecules} = \dfrac{\text{Mass in grams [of nitrogen]}}{\text{Rel. molecular mass [Mol. wt.]}} \\[0.5em] = \dfrac{21}{28} \\[0.5em] = 0.75 \text { gram molecules}$

Hence, gram molecules in 21 g of nitrogen = 0.75 gram molecules