Consider an ideal heat pump and a perfect electric heater. The electric heater convert100% of the electrical energy into heat energy; the heat pump convert 100% of the electrical energy into work, which then powers a Cannot refrigerator. Which is the more “efficient “ way to heat a home? (Ignore maintenance or start-up costs.)(A) The electric heater is always more efficient.(B) The heat pump is always more efficient. (C) The heat pump is more efficient if the outside temperature is not too warm.(D) The heat pump is more efficient if the outside temperature is not too cold.

The correct option is (C).
A heat pump is a device that acting as a Carnot refrigerator can heat a house by transferring heat energy from the outside to the inside of the house; the process is driven by work done on the device. So, heat pump, which is also a refrigerator, is an air conditioner that can be operated in reverse to heat room. By heating the room using a perfect electric heater, there is some loss of thermal energy due to heating the coil of the electric heater.
The value of coefficient of performance K becomes larger as the temperature of the two reservoirs becomes more nearly the same. Thus heat pumps are more efficient in temperate climates than in climates where the outside temperature fluctuates between wide limits. From the above observation we conclude that, the heat pump is more efficient if the outside temperature is not too warm. Thus option (C) is correct