Explanation

(a)
We know that molecular mass of hydrogen $\left( M_{1} \right) = 2$ and that of helium $\left( M_{2} \right) = 4.$ We also know that Graham’s law of diffusion
$\frac{r_{1}}{r_{2}} = \sqrt{\frac{M_{2}}{M_{1}}} = \sqrt{\frac{4}{2}} = \sqrt{2} = 1.4$
$r_{1} = 1.4\ r_{2}$