Which of the following processes does NOT involve a change in temperature?

In the context of thermodynamic processes, an isothermal process is characterized by a constant temperature throughout the entire process. This means that the system is allowed to exchange heat with its surroundings in such a way that, despite any work being done or material changes occurring, the temperature remains unchanged.

During an isothermal process, the internal energy of an ideal gas remains constant, as it is directly related to temperature. In contrast to isothermal processes, other processes such as isochoric (constant volume), isobaric (constant pressure), and adiabatic (no heat exchange) can involve temperature changes depending on the work done and the nature of the system.

This understanding of an isothermal process being defined by a constant temperature directly supports the rationale behind identifying it as the process that does not involve a change in temperature.