Thermodynamics

(a, b, d) From state I to II (Reversible isothermal expansion)
T→ constant, ∆V→+ ve, ∆S→+ ve, ∆H→0 P→− ve
From state II to III (Reversible adiabatic expansion)
q→0,∆V→+ ve,∆S→ constant
H→− ve, P→− ve, T→− ve
∴ Plots (a), (b), (d) are correct while (c) is wrong as form state II to III, H is decreasing.