Which of the following is a necessary condition for a process to be reversible?
(A) The substances undergoing a reversible change must at all instances be in thermodynamic equilibrium with its surroundings.
(B) All the processes taking place in the cycle of operation must be infinitely slow.
(C) There should not be any loss of energy due to conduction, convection or radiation during the cycle of operation.
(D) All of the above.

Hint: A thermodynamic process is reversible. If the process can be turned face such that both the system and the surroundings return to their original states, with no other change anywhere else in the universe.

Complete answer:
Conditions for Reversibility:
1. The substance undergoing a reversible change must at all instance be in thermodynamic equilibrium with its surroundings. It means the pressure and temperatures of the working substance must never differ appreciably from its surroundings at any stage of the cycle of operation.
All the processes taking place in the cycle of operation must be infinitely slow.
There should be a complete absence of frictional forces.
There should not be any loss of energy due to conduction, convection or radiation during the cycle of operation.

So, the correct answer is “Option D”.

Note:
In an adiabatic process, the system is insulated from the surroundings and heat absorbed or released in zero. An isothermal process is one in which the temperature is constant. A process is said to be irreversible if it cannot return the system and the surroundings to their initial states when the process is reversed. The irreversible process is not at equilibrium throughout the process. An isobaric is one is one in which the pressure is constant.