what's the difference between a nerve cell at the end of repolarization and a nerve cell in the resting state

The only difference between the end of the repolarization phase and the resting state is that the sodium and potassium ions are on the opposite sides from where they began.

The correct answer would be a. pacemaker.

A pacemaker is a medical device implanted in a chest or abdomen of a person suffering from arrhythmias (irregular heart rate; too fast, too slow, or irregular rhythm).

It is used in monitoring and maintaining a heart rate of a person.

It consists of a computerized generator, battery, and wires with sensors.

If an abnormal rhythm is detected by a device, it generates electrical impulses which help in contraction of heart muscles and thus, help in regulating the electrical conduction system of a heart.