I apologize for my answer here. The correct answer is d only i.e none of the above options A, B, C are wrong. The wording of question is tricky as it says, 'rise of x0 in equilibrium' which in itself implies quasi static expansion. In macroscopic thermodynamics we deal with systems having uniform properties. Thus, calculating work in non quasi static processes is not possible.
I realized my mistake as I started learning thermodynamics at IIT. It is being taught beautifully here.