What is the cell potential?
a-the difference in reduction potentials of the half-cells
b-the difference in oxidation potentials of the half-cells
c-the sum of reduction potentials of the half-cells
d-the sum of the oxidation potentials of the half-cells

For electrons to be transferred from the anode to the cathode, there must be some sort of energy potential that makes this phenomenon favorable. The potential energy that drives the redox reactions involved in electrochemical cells is the potential for the anode to become oxidized and the potential for the cathode to become reduced. The electrons involved in these cells will fall from the anode, which has a higher potential to become oxidized to the cathode, which has a lower potential to become oxidized. This is analogous to a rock falling from a cliff in which the rock will fall from a higher potential energy to a lower potential energy.

Must be negative.substance increases