Which one of the following gases has the same RMS velocity at $27^{\circ}C$ as that of $N_2$ with RMS velocity of $5.0 \times 10^4\: cm.s^{-1}$ at $7^{\circ}C$?

Question

$\begin {array} {1 1} (1)\;C_4H_{10} & \quad (2)\;C_2H_6 \\ (3)\;C_3H_8 & \quad (4)\;CH_4 \end {array}$