**Core Concept**
The resting membrane potential (RMP) of a nerve cell is primarily determined by the movement of ions across the cell membrane, particularly potassium (K+) and sodium (Na+). The Nernst equation is used to calculate the equilibrium potential for each ion, which is the electrical potential at which the concentration gradient of an ion is zero.

**Why the Correct Answer is Right**
The RMP is close to the equilibrium potential for potassium (EK), which is approximately -80 to -90 mV. This is because the cell membrane is more permeable to potassium ions than to sodium ions at rest. The high concentration of potassium ions inside the cell and their relatively low permeability across the cell membrane result in a negative equilibrium potential. The RMP is also influenced by the movement of sodium ions, but the equilibrium potential for sodium (ENa) is more positive (+60 mV), and the cell membrane is less permeable to sodium ions at rest.

**Why Each Wrong Option is Incorrect**
**Option A:** The equilibrium potential for chloride ions (ECl) is typically negative, but it is not the RMP of the nerve cell.
**Option B:** The equilibrium potential for calcium ions (ECa) is positive, but it is not directly related to the RMP of the nerve cell.
**Option C:** The equilibrium potential for hydrogen ions (EH) is not a relevant concept in this context, as the RMP is not determined by the movement of hydrogen ions.

**Clinical Pearl / High-Yield Fact**
The RMP is a critical factor in the generation and propagation of action potentials in nerve cells. Understanding the equilibrium potential for potassium ions is essential for grasping the underlying physiology of excitable cells.

**Correct Answer: C. The equilibrium potential for potassium ions.**