At 27∘C , H2 is leaked through a tiny hole into a vessel for 20 minute. Another unknown gas at the same T and P as that of H2 is leaked through the same hole for 20 minute. After the effusion of the gases, the mixture exerts a pressure of 6 atm. The H2 content of the mixture is 0.7 mole. If volume of container is 3 litre, what is molar mass of unknown gas? (IIT 1992)