The R.M.S. speed of the molecules of a gas of density 4 kg m^-3 and pressure 1.2 * 10⁵ N m^-2 is :

Rms=whole under root 3P/d.      Where P is pressure in pascal and d is density in kg/m^3. There fore.     Rms=whole underroot (3*1.2*10^5)/4.    = wholeroot 360000/4.                   This is equal to whole root90000.                                                                                           Therefore ans=300m/s