Which of the following is an example of a solid fuel combustion appliance?

A solid fuel combustion appliance is one that burns solid materials to produce heat. Fireplaces are a prime example of this, as they typically use wood or other solid fuels for combustion. This process generates heat through the burning of these materials, making fireplaces a classic representation of solid fuel combustion appliances.

Natural gas furnaces and heat pumps are not considered solid fuel appliances because they rely on gas or electricity, respectively, and do not involve the combustion of solid materials. Electric heaters, likewise, operate through electrical resistance and do not contain any combustion process at all. Therefore, a fireplace stands out as the example of a solid fuel combustion appliance.