Coal is best used as a

Fuel

Paint

Fertilizer

Conductor

A. Fuel.

Explanation:

Coal is extensively used as a fuel in many countries for the production of electricity. When coal is heated, the heat energy is used to convert the liquid water into steam which is used to move turbines in the electric power plant. When these turbines moves, the electricity is produced. This fossil fuel is also used for warming of rooms and cooking delicious foods.