I'm not asking about the specific questions contained in the attached document - I know all the answers. I'm wondering if this is even possible. A to B: free expansion (which I take always means "adiabatic free expansion"). B to C: adiabatic compression. Adiabatic means no heat is exchanged. So if system is returned to its original volume adiabatically, and no heat is exchanged, what -- physically -- could account for an increased pressure at C??