Final answer:
The resting membrane is much more permeable to potassium than sodium due to more leakage channels for potassium and the action of the sodium-potassium pump, which results in potassium being able to exit the cell more easily than sodium can enter.
Step-by-step explanation:
In a typical resting membrane potential, which is approximately -70 mV (millivolts), the cell membrane is significantly more permeable to potassium (K+) ions than to sodium (Na+) ions. This is primarily due to the presence of more potassium leakage channels compared to sodium leakage channels.
Potassium ions tend to leave the cell through channels that are open around 90% of the time, while sodium channels are rarely open, thus maintaining a high permeability to potassium.
The sodium-potassium pump actively contributes to this difference, by transporting two potassium ions into the cell for every three sodium ions it sends out, further affecting the distribution of these ions and reinforcing the negative charge inside the cell relative to its exterior.