For which one of these processes is Direct Current essential, and will not work with...

Direct Current (DC) is essential for the process of electrolysis. Electrolysis is the process of breaking down a compound using an electric current. The electric current causes ions to move, which results in a chemical reaction that breaks down the compound. In order for electrolysis to work, a direct current is required, as the ions must flow in one direction. Alternating Current (AC) changes direction and would not provide a consistent flow of ions.

Heating, lighting, and turning a motor can be done by either DC or AC. Heating can be done by passing an electric current through a heating element, which can be powered by either DC or AC. Lighting can be done by passing an electric current through a light bulb, which can be powered by either DC or AC. A motor can be powered by either DC or AC, but the type of motor and the application will determine which type of current is more suitable.