This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, 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. Does not help other ions in transport
C: Responsible for Depolarization
Answer: C: Responsible for Depolarization 
Explanation: Depolarization occurs due to sodium ions influx.
Potassium ions maintain the resting membrane potential.
Sodium ions are not responsible for Gibbs-Donnan effect. It is due to the non-diffusible anions.
Sodium ions take part in many co-transports.