The Sodium Level Inside and Outside of a Resting Cell

The sodium level inside and outside of a resting cell is an example of the

A) kinetic energy of sodium rushing out of a cell down its concentration gradient.
B) kinetic energy of the large difference in sodium concentration on the inside versus the outside of the cell.
C) potential energy of a concentration gradient, because sodium is more abundant outside the cell.
D) potential energy of an electron transport chain, because sodium has an extra electron to donate.
E) conversion of potential energy to kinetic energy, because sodium can never move across the cell membrane and must move across its surface.