The answer is; B.
The resting potential of most neurons is usually -70mV. When depolarization begins and approximately the neuron is depolarized to approximately – 55mV to 50mV, an impulse is initiated in the neuron. This action potential is characterized by remarkably rapid depolarization that is cascaded down the neuron axon. Depolarization involves the influx of sodium and potassium ions making the inside of the neuron cells less and less negative.