∵N2O4⇌2NO2 Molar ratio =1:2 Also, only 20% of N2O4 gets decomposed means. 1 mole of N2O4 on dissociation give =0.2×2=0.4 moles of NO2 and 0.8 moles of N2O4 remain undissociated. Thus, Total number of moles at equilibrium =0.4+0.8=1.2 moles ∵ Total pressure (pt)=1atm (given) According to Daltons law of partial pressure Partial pressure of N2O4=X(N2O4)×pt and partial pressure of NO2=X(NO2)×pt Partial pressure of NO2=