Q.The temperature of the system decreases in an ___________________

Step 1. Isothermal processes (a, b) keep temperature CONSTANT by definition (Section 7.2.3) -- they cannot show a temperature decrease at all.

Step 2. In an adiabatic process $q=0$ (Section ~7.2.5/7.4.1): if the gas EXPANDS, it does work on its surroundings, and since no heat can flow in to replace that lost energy, its own internal energy -- and hence temperature -- f …

Rule out the two isothermal options immediately (temperature is fixed by definition), then decide between adiabatic …

• Picking adiabatic compression, which raises temperature, not lowers it -- the t …