## **Core Concept**
The resting membrane potential (RMP) is the difference in electrical charge between the inside and outside of a neuron when it is not being stimulated. This potential is primarily generated by the movement of ions across the cell membrane. The main ions involved in generating the RMP are potassium (K+), sodium (Na+), and to a lesser extent, chloride (Cl-).

## **Why the Correct Answer is Right**
The resting membrane potential is mainly due to the **high permeability of the membrane to potassium ions (K+)** and the action of the **sodium-potassium pump**. The cell membrane at rest is more permeable to K+ than to Na+ or Cl-. Potassium ions tend to leave the cell down their concentration gradient, which is maintained by the sodium-potassium pump. This pump actively transports 3 Na+ out of the cell and 2 K+ into the cell, using ATP for energy. As K+ ions leave the cell, they carry positive charge with them, making the inside of the cell more negative relative to the outside. This process results in a negative resting membrane potential, typically around -70 mV.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while sodium (Na+) does play a role in the generation of the action potential, its contribution to the resting membrane potential is minimal due to the low permeability of the resting membrane to Na+.
- **Option B:** This option is incorrect because chloride (Cl-) does influence the resting membrane potential, especially in certain types of neurons, but it is not the main contributor.
- **Option D:** This option is incorrect because, although the sodium-potassium pump is crucial for maintaining the ion gradients that allow the resting membrane potential to be generated, the immediate cause of the RMP is the diffusion of ions, primarily K+, across the membrane.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the resting membrane potential is generated primarily by the movement of potassium ions out of the cell. The **Nernst equation for potassium** can be used to estimate the resting membrane potential, which is given by (E_{K+} = frac{RT}{zF} lnleft(frac{[K+]_{outside}}{[K+]_{inside}}right)). This equation highlights the importance of the potassium gradient in determining the RMP.

## **Correct Answer:** .