Explanation

(c)
$u = \sqrt{\frac{3RT}{M}}$
$u_{H_{2}} = \sqrt{\frac{3RT_{H_{2}}}{M}}\ ;u_{N_{2}} = \sqrt{\frac{3RT_{N_{2}}}{M}}$
$\sqrt{\frac{3RT_{H_{2}}}{M}} = \ \sqrt{7} \times \sqrt{\frac{3RT_{N_{2}}}{M}}$
$\left( \begin{array}{r}
because\ rms\ speed\ of\ H_{2}\ is\ \sqrt{7}\ times\ the\ rms\ \\
speed\ of\ N_{2}
\end{array} \right)$
$\frac{3RT_{H_{2}}}{M} = 7 \times \frac{3RT_{N_{2}}}{M}$
$\frac{T_{H_{2}}}{2} = \frac{7 \times T_{N_{2}}}{28}$
$\frac{T_{H_{2}}}{14} = \frac{T_{N_{2}}}{28}$
or $\ \ \ T_{H_{2}} < T_{N_{2}}$