Final answer:
In a reversible adiabatic process, the change in entropy is zero, but such processes in real macroscopic systems are not perfectly reversible due to unavoidable energy dissipation.
Step-by-step explanation:
The change in entropy in an adiabatic process is typically zero if the process is reversible. This implies that adiabatic processes can be reversible in principle, but it is crucial to understand that this reversibility is an idealization. In reality, due to dissipative forces such as friction or turbulence, adiabatic processes in macroscopic systems are not perfectly reversible because they cannot be returned to their exact initial states without changing the surroundings. Moreover, although the entropy of individual parts of an isolated system may change during a reversible process, the total change in entropy for the system and its environment combined is zero. In a real, irreversible adiabatic process, however, the total entropy of the system and its surroundings can increase.
To answer the question, the correct choice is: b) The change in entropy is zero; adiabatic processes are not reversible. While in theory, reversible adiabatic processes do not change the total entropy, in practice, perfect adiabatic reversibility is not attainable for a macroscopic system due to unavoidable energy losses to the surroundings.