c
Given:- $rm s$ speed of the gas moLecules Half of the gas leaks $=400 \; m / s$. we need to find the $V_{rms}$ of remaining molecules. we need to find the $V_{r m s}$ of remaining molecules.
$V_{\text {rms }}=\sqrt{\frac{3 R T}{M}}$ whene $T=$ temperature.
It is given that half of the gas moleculles leaks out.
Since there is no role of number of molecules in $rms$ speed, therefore the final speed will remain the same
$\therefore 400 \; m / s$