The rms speed of molecules in hydrogen gas is
$$
v_{\mathrm{rms}}=\sqrt{\frac{3 k_B T}{m}}
$$
where,
$m=$ mass of hydrogen,
$k_B=$ Boltzmann's constant
and $T=$ temperature in kelvin.
$$
\therefore \quad v_{\text {rms }} \propto \sqrt{T}
$$
Initial temperature, $T_1=(27+273 \mathrm{~K})=300 \mathrm{~K}$
If initial rms speed be $v_1$.
Final rms speed, $v_2=2 v_1$ at temperature $T_2$.
$$
\begin{aligned}
& \therefore & \frac{v_1}{v_2} & =\sqrt{\frac{T_1}{T_2}} \\
& \Rightarrow & \left(\frac{v_1}{2 v_1}\right)^2= & \frac{T_1}{T_2} \\
& \Rightarrow & T_2 & =4 T_1=4 \times 300 \mathrm{~K}=1200 \mathrm{~K} \\
& \therefore & T_2 & =(1200-273)^{\circ} \mathrm{C}=927^{\circ} \mathrm{C}
\end{aligned}
$$