Final answer:
The K+ equilibrium potential is characterized by the K+ concentration being 30 times higher inside the cell than outside, contributing to an Ek of approximately -90 mV, while the sodium-potassium pump maintains this gradient.
Step-by-step explanation:
The correct statement characterizing the K+ equilibrium potential (Ek) for a typical cell would be that the concentration of K+ is 30 times higher within the cell than in the extracellular fluid. This high concentration gradient is maintained by the sodium-potassium pump, which actively transports K+ ions into the cell while moving Na+ ions out, thereby also contributing to the negative electrical charge inside the cell.
The Ek, typically around -90 mV, denotes the electric potential difference across the cell membrane that balances the K+ concentration gradient when the cell is at rest, preventing further net movement of K+ across the membrane. It is important to note that while K+ can leak out of the cell through K+ channels, Na+ channels are less permeable, retaining the high Na+ concentration outside the cell.