Final answer:
Increasing the external Na+ concentration from 150mM to 200mM with Na+ being permeable will lead to more Na+ flowing into the cell and causing depolarization, moving the membrane potential towards a more positive value.
Step-by-step explanation:
If the outside concentration of Na+ changes from 150mM to 200mM and Na+ is permeable, there will be an increase in the concentration gradient causing more Na+ ions to rush into the cell. This influx of positively charged sodium ions will result in depolarization of the cell's membrane potential, moving it from a resting voltage of -70 mV towards zero and potentially above, becoming more positive. Normally, the membrane is less permeable to Na+, but if it is permeable, the effect on the membrane potential will be significant, possibly reaching up to +30 mV as sodium continues to enter the cell driven by both the concentration gradient and the electrical gradient due to negative proteins below the membrane.