When the refrigerant enters the throttling valve it expands and release pressure.Consequently, the temp drops at this stage. Because of these changes the refrigeration leaves the throttles valve as liquid vapour mixture. Throttling valves play two critical roles in the vapour compression cycle.

1. They maintain a pressure differential between low and high pressure side.

2. They control the amount of liquid refrigerant entering the evaporator.

The expansion process in the throttling device of a vapour compression cycle is isenthalpic process.

The vapor-compression system consist of four processes :

Process 1 – 2 : Isentropic compression of saturated vapour in compressor

Process2 – 3 : Isobaric heat rejection in condenser

Process3 – 4 : Isenthalpic  expansion of saturated liquid in expansion valve

Process4 – 1 : Isobaric heat extraction in the evaporator

Hence, the correct option is (C).