Study the following table: Fuel Calorific value State Ignition temp. A High…

A good domestic fuel should ideally have three qualities: a high calorific value, so it releases plenty of heat per unit mass; a gaseous state, since gaseous fuels burn cleanly without leaving behind ash or soot and their flow can be started, stopped, and adjusted with ease; and a moderate ignition temperature, high enough to stay safe during storage and transport, yet low enough to be lit without difficulty.

None of the four listed fuels combines all three qualities perfectly, so the best domestic fuel is the one that comes closest overall. Fuel C is gaseous, so it burns cleanly, and its ignition temperature is moderate, so it lights easily while remaining safe to store. Its calorific value is only moderate rather than high, but this is still the best balance among the options offered, since each of the other three fuels fails on a more serious count.

• Fuel A has a high calorific value but is solid, so it leaves behind ash and soot, and its high ignition temperature makes it difficult to light for everyday use.

• Fuel B is gaseous, like Fuel C, but its high ignition temperature makes it difficult to ignite reliably in a home burner.

• Fuel D has a low calorific value, so it releases comparatively little heat, and its low ignition temperature is a fire-safety hazard since it can catch fire too easily during storage.

Weighing all three factors together, Fuel C offers the best overall combination among the four options - clean gaseous burning plus a safe, easy-to-light ignition temperature - so it is best suited as a domestic fuel, even though its calorific value is moderate rather than the highest of the four.