Answer : 2.01 $ \times$ 10$^{4}$ K

$v_{rms} =\sqrt{ \large\frac{ 3RT}{M}}$$ = 11.2 \times 10^3\; m/s$

$\Rightarrow T = \large\frac{v_{rms}^2 \times M}{3r}$$ = \large\frac{(11.2\times 10^3)^2 \times 4 \times 10^{-3}}{3 \times 8.315}$$ = 2.01 \times 10^4\;K$