Final answer:
The net movement of Na+ into the cell will continue until either the Na+ channels close or the membrane potential reaches the equilibrium potential for Na+, typically at around +30 to +60 mV. Option (D) 'either B or C' is correct.
Step-by-step explanation:
If a cell is at rest (-70 mV) and ligand-gated Na+ channels open, there will be a net movement of Na+ into the cell until few conditions are met. When sodium ions (Na+) rush into the cell, due to the higher concentration outside, they are primarily driven by the concentration gradient. This influx of positively charged ions depolarizes the membrane potential, leading it to become less negative (a move toward zero). The presence of Na+ influx will continue because of the strong concentration gradient until the electrical gradient, influenced by negatively charged proteins, becomes a factor. The influx of Na+ can depolarize the membrane potential up to around +30 mV.
Given the states provided in the question, the net movement of Na+ into the cell will continue until either (B) the Na+ channels close or (C) the membrane potential reaches the equilibrium potential for Na+, which is typically around +30 to +60 mV. Option (D) 'either B or C' is the correct answer as either closing the sodium channels or reaching the equilibrium potential will halt the movement of Na+ into the cell.