**Core Concept**
The resting membrane potential of a nerve cell is primarily determined by the movement of ions across its cell membrane. At rest, the cell membrane is more permeable to potassium ions (K+) than to other ions. This results in a net flow of potassium ions out of the cell, creating a negative charge inside the cell.

**Why the Correct Answer is Right**
The equilibrium potential for chloride ions (Cl-) is closest to the resting membrane potential of a nerve cell. This is because the chloride ion equilibrium potential (ECl) is determined by the Nernst equation, which takes into account the concentration of chloride ions inside and outside the cell. At rest, the concentration of chloride ions inside the cell is relatively high compared to other ions, making the ECl closer to the resting membrane potential. In contrast, the equilibrium potential for sodium ions (ENa) is more positive than the resting membrane potential, while the equilibrium potential for potassium ions (EK) is more negative.

**Why Each Wrong Option is Incorrect**
**Option A:** Sodium ions (Na+) have a high concentration outside the cell and a low concentration inside, resulting in an equilibrium potential (ENa) that is more positive than the resting membrane potential.
**Option C:** Potassium ions (K+) have a high concentration inside the cell and a low concentration outside, resulting in an equilibrium potential (EK) that is more negative than the resting membrane potential.
**Option D:** Bicarbonate ions (HCO3-) play a crucial role in maintaining the acid-base balance in the body, but they do not have a significant effect on the resting membrane potential of a nerve cell.

**Clinical Pearl / High-Yield Fact**
The resting membrane potential is a critical determinant of neuronal excitability, and changes in ion concentrations or membrane permeability can lead to alterations in the resting membrane potential, affecting neural function.

**✓ Correct Answer: B. Cl-**