d
(d) Speed of sound in gases is $v = \sqrt {\frac{{\gamma RT}}{M}} $==> $T \propto M$
(Because $v,$ $\gamma$-constant).
Hence $\frac{{{T_{{H_2}}}}}{{{T_{{O_2}}}}} = \frac{{{M_{{H_2}}}}}{{{M_{{O_2}}}}}$
==> $\frac{{{T_{{H_2}}}}}{{(273 + 100)}} = \frac{2}{{32}}$
==> ${T_{{H_2}}} = 23.2K = - 249.7^\circ C$