i think we just need to apply root(3RT/M)  also gases behave ideally at high temp & low pressure .. the given pressure can be assumed to be low compared to 760 mm Hg pressure(atm pressure) ........

 

 if the the gas was to be considered non ideal then the question will surely give the compressibilty factor then apply this eqn to calculate rms velocity > root(3ZPV/M) , where Z is the compressibilty factor at that temp.

 

thnx