[orgo814]

For this question, the answer is C. I understand that the delta H vap = 0 at critical point so it should move to zero but why is B not an acceptable answer here

[mjc123]

ΔH_vap (or should I say Δ_vapH?) does not vary linearly with temperature. Over much of the liquid range it varies only slowly, but changes more rapidly as the critical point is approached.