The isothermal and adiabatic processes are regarded as reversible processes.

Explanation:
- The isothermal process is a thermodynamic process that occurs at constant temperature. In an isothermal process, the heat exchange occurs in such a way that the temperature of the system remains constant throughout the process. This is achieved by maintaining a thermal equilibrium between the system and its surroundings. In other words, the system absorbs heat from its surroundings while expanding and releases heat to its surroundings while compressing. Since the temperature remains constant, the system always remains in equilibrium with its surroundings, making the process reversible.

- The adiabatic process is a thermodynamic process that occurs without any heat exchange between the system and its surroundings. In an adiabatic process, the system is thermally isolated, meaning no heat is transferred in or out of the system. As a result, the temperature of the system can change during the process. However, for the process to be reversible, the system must be able to return to its initial state by reversing the process. This can only be achieved if the process is quasi-static and there are no irreversibilities, such as friction or heat transfer, present. Therefore, an adiabatic process that is also quasi-static is considered to be reversible.

Reversible Processes:
- A reversible process is one in which the system can be restored to its initial state by infinitesimally small changes in the external conditions. Reversible processes are idealized and do not occur in practice, but they serve as a useful theoretical concept for understanding thermodynamic systems. In a reversible process, the system and its surroundings can be brought into equilibrium at every stage of the process. This means that the system can be returned to its initial state without leaving any trace on the surroundings or the system itself.

Irreversible Processes:
- Irreversible processes are those that do not satisfy the conditions for reversibility. In an irreversible process, the system and its surroundings cannot be brought into equilibrium at every stage of the process. Irreversible processes are characterized by the presence of irreversibilities, such as friction, heat transfer through finite temperature differences, and other dissipative effects. These irreversibilities lead to an increase in the entropy of the system and its surroundings, making the process irreversible.

Conclusion:
- Both the isothermal and adiabatic processes are regarded as reversible processes because they satisfy the conditions for reversibility. In the case of an isothermal process, the constant temperature ensures that the system remains in thermal equilibrium with its surroundings throughout the process. In the case of an adiabatic process, the absence of heat transfer allows the system to return to its initial state if the process is reversed.