One mole of N2O4at 300K is kept in a closed vessel at 1 atm. It is heated to 600K when 20% by mass of N2O4 (g) decomposes to NO2(g).  The resultant equilibrium pressure is

N2O4⇌2NO21                                  01−x                        2x1−0.2                 2×0.20.8                             0.4PT=0.8+0.4=1.2P1V=n1RT1P2V=n2RT2P1P2=n1T1n2T21P2=1×3001.2×600P2=2.4atm