This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General, Subject name: Physiology
True regarding Na+ ion 
Select and explain. 
A. Responsible for Donnan effect, B. Responsible for resting membrane potential, C. Responsible for depolarization, D. Dose not help other ions in transport
C: Responsible for depolarization
Answer: C: Responsible for depolarization 
Explanation: Ans. (c) Responsible for depolarization(Ref: Guyton, 13th ed/p.65)Option a - Sodium ion is not Responsible for Donnan effect. This effect is due to non-diffusible anions like proteinsOption b - potassium ion is responsible for RMPOption d - many substances require sodium for their transport through secondary active transport processes