This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
The electrical potential difference necessary for a single ion to be at equilibrium across a membrane is best described by the 
Select and explain. 
A. Goldman equation, B. van't Hoff equation, C. Fick's law, D. Nernst equation
D: Nernst equation
Answer: D: Nernst equation 
Explanation: At normal body temperature (37degC), the electrical difference that will balance a given concentration difference of univalent ions--such as Na+ ions--can be determined from the following formula, called the Nernst equation.Ref: Guyton; 13th edition; Chapter 4 Transpo of Substances Through Cell Membranes