Q.

The square root of the mean of the squares of speeds of all gas molecules is called its RMS speed.
${\mathrm{U}}_{\mathrm{rms}}=\sqrt{\frac{{\mathrm{U}}_1^2+{\mathrm{U}}_2^2+\dots \dots +{\mathrm{U}}_{\mathrm{n}}^2}{\mathrm{n}}}=\sqrt{\frac{3\mathrm{RT}}{\mathrm{M}}}$