Two types of electrochemical cells which are based on thermodynamic principles can be described. Which of the following statements about these cells is correct?
A. The current in the external wire flows from cathode to anode in both cells.
B. Oxidation occurs at the cathode only in the voltaic cell.
C. The free energy change, ?G, is negative for the electrolytic cell.
D. The cathode is positive in a voltaic cell but negative in an electrolytic cell.