Answer: option B is correct.
Step-by-step explanation:
Okay let us fill in the gap in the question;
"In a resting state, sodium (Na+) "is at a higher concentration outside the cell and potassium (K+) is more concentrated inside the cell. During an action potential, the sodium levels INCREASE inside the cell''.
The answer is option B. The levels of sodium inside the cell increase because Sodium (Na^+) enters while the potassium (K^+) moves out of the cell and NOT that the sodium(Na^+) leaves/moves out of the cell. The Sodium(Na^+) outside the content of the cell is more positive than the the content of the cell, this will enhance the sodium ion(Na^+) to move inside the cell thereby INCREASING the sodium levels in the cell.