Answer:
The correct answer would be "Its cytoplasm becomes more positive, and its plasma membrane becomes more negative".
At rest, the outer membrane of the axon possesses a positive charge while the inner surface possesses a negative charge. This condition is termed as polarized and the potential difference across the plasma membrane is termed as resting membrane potential.
When the neuron is stimulated, axon membrane becomes freely permeable to sodium ions which results in the rapid influx of the sodium ions. It results in the reversal of polarity of the membrane that is, now the inner membrane becomes positive and the outer membrane becomes negative. Thus, this condition is called depolarized and the potential difference is termed as an action potential.
