Initially, the $root\; mean\; square\; (rms)$ velocity of $N2$ molecules at certain temperature is $u$. If this temperature is doubled and all the nitrogen molecules dissociate into nitrogen atoms, then the new $rms$ velocity will be :

Question

$\begin{array}{1 1}(1) u/2 \\(2) 2u\\ (3) 4u \\(4) 14u \end{array}$