The Carnot device operates as a refrigerator in all scenarios since the heat source is always at a lower or equal temperature than the heat sink. Thus, the work done is not used to generate work but for refrigeration in each case.
The work done by a Carnot device that extracts 5 kJ of heat from a body at -10°C and exhausts heat into the environment at different temperatures depends on whether the device operates as an engine or a refrigerator and the temperature difference between the heat source and the sink. The operation mode of the Carnot device is determined by the direction of heat flow, which depends on the temperatures of the bodies involved.
For scenario (a) at 25°C, the heat source is at a lower temperature than the sink, hence the Carnot device functions as a refrigerator. For scenario (b) at 0°C, the device can't operate as an engine since there's no temperature gradient to drive the engine; it would also act as a refrigerator due to the heat source being colder. For scenario (c) at -25°C, the heat is being transferred from a colder to a warmer body, allowing the device to work as a refrigerator. Therefore, the correct answer is:
Option C: a) 14.7 kJ (refrigerator), b) 20 kJ (refrigerator), c) 16.7 kJ (refrigerator).