This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pharmacology
The electrical potential difference necessary for a single ion to be at equilibrium across a membrane is best described by the (NOT RELATED) 
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: .