The value of Kp for the equilibrium of the reaction N2O4--------->2NO2 is 2 the the % dissociation of N2O4 at 0.5 atm pressure will beA.25B.68C.71D.82Please help!

I am not writing the detailed answer but it is some where near to 68, i.e. B, however trick is to calculate the value of α by taking initial pressure of N₂O₄ 0.5-(0.5alpha)....and then clalculate alpha by given K_p

the value comes out to be 70.92(approx.) hence the correct value is 71(most appropriate here) ,hence C is correct.

I wanted help with the method to solve it.Could you give the method in brief