Which of the following processes occurs in a gas cycle?

In a gas cycle, specifically in the context of thermodynamic cycles such as the Brayton cycle used in gas turbines, the key process involves the combustion of fuel with air. This process is critical as it generates high-temperature, high-pressure gases that expand and do work on a turbine, converting thermal energy into mechanical energy.

During this combustion process, fuel, often a hydrocarbon, reacts with an oxidizer, typically atmospheric air, resulting in the production of hot exhaust gases. This energy release is fundamental to the cycle, as it provides the necessary energy input for the expansion phase that follows.

The other processes mentioned relate to different cycles or refrigeration systems. For instance, condensation of steam is associated with the Rankine cycle, which involves phase changes of water; compression of refrigerants pertains to refrigeration cycles where heat is absorbed and removed through phase changes; and cooling through evaporation typically describes a heat transfer mechanism found in evaporative cooling systems. Each of these processes operates under different thermodynamic principles and thus does not fit into the gas cycle context as the combustion process does.