The behaviour of real gas approaches ideal behaviour at

The ratio of average velocity of a gas molecule to the root mean square velocity at a particular temperature is

What is the molecular mass of X if the rate of diffusion of methane is twice that of X.

What will be the density of N$$_2$$ gas at 230$$^\circ$$C and 3 atm pressure? (R = 0.082 L atm K$$^{-1}$$ mol$$^{-1}$$)