In reaction, C(s)+CO2(g)⇌2CO(g) , the equilibrium pressure is 12 atm. If 50% CO2  reacts, Kp  is x2 atm. Hence x  is

C(s)+CO2(g)⇌2CO(g) Eq partial pressure        a−a2                         a  a+a2=12 ∴a=12×23=8atm Kp=8×84=16atm=42atm