The correct answer is (a).
The coefficient of performance (COP) of a heat pump is the ratio of the heat output to the work input. The COP of a refrigerator is the ratio of the heat removed from the cold space to the work input.
The COP of a heat pump is always greater than or equal to 1, while the COP of a refrigerator is always less than or equal to 1. This is because a heat pump can move heat from a low temperature to a high temperature, while a refrigerator can only move heat from a high temperature to a low temperature.
Option (b) is incorrect because the COP of a heat pump is not always greater than 10. The COP of a heat pump depends on the temperature difference between the heat source and the heat sink. The larger the temperature difference, the lower the COP of the heat pump.
Option (c) is incorrect because the COP of a heat pump is not always greater than 100. The COP of a heat pump depends on the temperature difference between the heat source and the heat sink. The larger the temperature difference, the lower the COP of the heat pump.
Option (d) is incorrect because the COP of a heat pump is not always negative. The COP of a heat pump is always greater than or equal to 1.