How is an electrolytic cell different from a voltaic cell?
electrons are gained at the anode in an electrolytic cell.
oxidation occurs at the cathode in an electrolytic cell.
a power supply is needed in an electrolytic cell.
a salt bridge is needed in an electrolytic cell.

C is the correct answer. A voltaic cell is an electrochemical cell that uses a chemical reaction to produce electrical energy. An electrolytic cell is an electrochemical cell that drives a non-spontaneous redox reaction through the application of electrical energy, but it needs a power source.