The degree of dissociation of l2 molecule of 1000oC and under atmospheric pressure is 40% by volume. If the dissociation is reduced to 20%  at the same temp. total equilibrium pressure on the gas is :

I2(g) ⇌ 2I-(g) t=0, 1mol        0 teq.;   1-x        2x n=1-x+2x=1+x Kp=PI-2PI2=2x1+xP21-x1+xP=4x21-x2P Kpat 40%dissociation=Kpat 20%dissociation 4(0.4)21-(0.4)2P=4(0.2)21-(0.2)2P' given, P=1atm. , P'=? on solving, P'=4.57atm.