Which type of cell requires external power to drive a reaction?

• A. Battery
• B. Galvanic cell
• C. Electrolytic cell
• D. Fuel cell

Answer: (C)

External power to drive a reaction is the defining feature of an electrolytic cell. Here, a direct current power source forces electrons to flow in a direction that the chemistry would not favor on its own, pushing a non-spontaneous redox reaction forward. The oxidation occurs at the anode and the reduction at the cathode, with the anode connected to the positive terminal of the external source and the cathode to the negative terminal. This setup is used for processes like electrolysis or electroplating, where you steer the reaction by supplying energy. By contrast, galvanic cells (and devices like batteries and most fuel cells) generate electricity from spontaneous redox reactions and do not require external power to operate; a battery stores chemical energy, and a fuel cell produces electricity as long as reactants are supplied.