Final answer:
The resting membrane potential is closest to the equilibrium potential for potassium ions (K+), due to the neuron's membrane's selective permeability and the activity of the sodium-potassium pump.
Step-by-step explanation:
The resting membrane potential is most closely associated with the equilibrium potential of potassium ions (K+). The resting potential of a neuron, usually around -70 millivolts (mV), is dependent on the distribution of ions across its membrane. Particularly, potassium ions have a high concentration inside the cell, and the membrane is more permeable to K+ than to sodium ions (Na+).
K+ ions diffuse out of the neuron through potassium leakage channels, resulting in a net negative charge inside the cell. This activity helps to establish the resting membrane potential. The sodium-potassium pump also plays a critical role by pumping two K+ ions into the cell and three Na+ ions out of the cell for each ATP molecule consumed, further contributing to the cell's negative charge inside relative to the outside.