Which of the following does not describe conditions that occur during an action potential?
a) the na+/k+ pump reestablishes resting concentration gradients.
b) after initial depolarization, k+ now has both an electrical and a chemical gradient drawing it out of the cell.
c) na+ enters the cell through voltage-gated channels, causing a reversal of the resting membrane potential.
d) na+ is used to repolarize the membrane.

D) Na+ is used to repolarize the membrane.

Explanation:

Option D is wrong choice because it is K+ which is used to repolarize the membrane not Na+.

As soon as membrane gets depolarized because of influx of Na+ due to opening of voltage gated Na+ channels simultaneous opening of voltage gated K+ channels and closing of Na+ voltage gated channels takes place. As a result of which K+ moves out of the cell leading to drawing of electrochemical gradient out of the cell.

In order to achieve resting membrane potential, more Na+ must be out of the cell and more K+ must be inside the cell. There are many leaky channels on neurons from which Na+ has tendency to leak into the cell while K+ has the tendency to leak outside of the cell. So Na+/K+ pump which is located on the membrane of neuron keeps pushing Na+ outside of the cell and K+ inside the cell so as to maintain resting membrane potential which is -70 mV.