This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Membrane potiential, Subject name: Physiology
Among the ions mentioned, the highest equilibrium potential is for: 
Select and explain. 
A. Na+, B. K+, C. Ca++, D. H+
C: Ca++
Answer: C: Ca++ 
Explanation: Equilibrium potential for Ca2+ = +129 mV. Two factors are responsible for this high value: 1.Calcium is a divalent cation. 2.Its concentration gradient (ECF:ICF) is very large.