Final answer:
During depolarization, the charge across the nerve cell membrane increases as Na+ channels open and positive sodium ions enter the cell, causing the inside to become less negative.
Step-by-step explanation:
When a nerve cell depolarizes, the charge across the cell membrane increases. Initially, the nerve cell membrane has a resting potential, usually around -70 mV, with the inside of the cell having a negative charge relative to the outside. During depolarization, Na+ channels open, allowing sodium ions to rush into the cell. This influx of positively charged Na+ ions decreases the negativity inside the cell, causing the membrane potential to move toward zero and even become slightly positive momentarily. This change in membrane potential results in the interior of the neuron becoming less negative compared to the outside, which is referred to as depolarization. The correct answer to what happens to the charge across the cell membrane during depolarization is that it increases, correlating with option 3 of the provided choices.