Reversed Carnot Cycle:
The reversed Carnot cycle is a theoretical thermodynamic cycle that consists of four processes: two isothermal processes and two adiabatic processes. It is a reversed version of the Carnot cycle, which is the most efficient thermodynamic cycle for a heat engine.

Working Principle of a Heat Pump:
A heat pump is a device that transfers heat from a low-temperature source to a high-temperature sink. It operates on the principle of the reversed Carnot cycle, where work is done on the system to transfer heat from a cold reservoir to a hot reservoir.

Coefficient of Performance (C.O.P.):
The coefficient of performance (C.O.P.) is a measure of the efficiency of a heat pump or refrigerator. It is defined as the ratio of the desired output (refrigeration effect or heating effect) to the required input (work done).

Calculating the Refrigerating Effect:
Given that the C.O.P. of the heat pump is 5 and it takes 1 kW of work input, we can calculate the refrigerating effect using the formula:

C.O.P. = Refrigerating Effect / Work Input

Substituting the given values:

5 = Refrigerating Effect / 1

Refrigerating Effect = 5 * 1

Refrigerating Effect = 5 kW

Therefore, the refrigerating effect of the heat pump is 5 kW.

Explanation:
The refrigerating effect of a heat pump is the amount of heat that is transferred from the cold reservoir to the hot reservoir. In this case, the heat pump has a C.O.P. of 5, which means that for every 1 kW of work input, it can transfer 5 kW of heat. Since the question states that the heat pump works as a refrigerator and takes 1 kW of work input, the refrigerating effect will be 5 kW.

The correct answer is option 'D' (4 kW), as stated in the question.