The equilibrium potential for sodium is

**Core Concept**
The equilibrium potential for sodium (E_Na) is a fundamental concept in physiology, representing the electrical potential at which the concentration gradient for sodium ions across a cell membrane is exactly balanced by the electrical gradient. This concept is crucial in understanding how neurons and other excitable cells generate action potentials.

**Why the Correct Answer is Right**
The equilibrium potential for sodium is determined by the Nernst equation, which takes into account the concentration of sodium ions inside and outside the cell, as well as the temperature and the gas constant. In a typical mammalian neuron, the concentration of sodium ions is about 10-20 times higher outside the cell than inside. According to the Nernst equation, the equilibrium potential for sodium is calculated as E_Na = (RT/F) * ln([Na+]_out / [Na+]_in), where R is the gas constant, T is the temperature in Kelvin, F is the Faraday constant, [Na+]_out is the concentration of sodium ions outside the cell, and [Na+]_in is the concentration of sodium ions inside the cell. This results in an equilibrium potential for sodium that is typically around +60-70 mV.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a numerical value or a range of values for the equilibrium potential for sodium. The equilibrium potential for sodium is a specific value that depends on the concentration of sodium ions inside and outside the cell.

**Option B:** This option is incorrect because it suggests that the equilibrium potential for sodium is around -60 mV, which is actually the equilibrium potential for potassium (E_K). The equilibrium potential for potassium is typically around -80-90 mV in a typical mammalian neuron.

**Option C:** This option is incorrect because it suggests that the equilibrium potential for sodium is around 0 mV, which is not accurate. The equilibrium potential for sodium is typically around +60-70 mV, not 0 mV.

**Option D:** This option is incorrect because it suggests that the equilibrium potential for sodium is around +100 mV, which is too high. The equilibrium potential for sodium is typically around +60-70 mV, not +100 mV.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the equilibrium potential for sodium is a critical parameter in understanding how neurons and other excitable cells generate action potentials. This concept is crucial in understanding various neurological disorders, such as epilepsy, where abnormal electrical activity in the brain can lead to seizures.

**Correct Answer:** . +65 mV