Enthalpy Change

For the reversible isothermal expansion from state I to II:

• Pressure decreases
• Volume increases
• Temperature remains constant
• Enthalpy (H) remains constant
• Entropy (S) increases

So, all options are correct for this expansion.

For the reversible adiabatic expansion from state II to III:

• Pressure decreases
• Volume increases
• Temperature decreases
• Enthalpy (H) decreases
• Entropy (S) remains constant

Option (C) does not follow the condition of decreasing enthalpy, so it is incorrect. Options (A), (B), and (D) all follow the conditions, so they are correct.

Therefore, correct graphical representations for the given conditions are (A), (B), and (D).