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
Most osmotically active intracellular cation 
Select and explain. 
A. K+, B. Na+, C. Mg+2, D. Protein
A: K+
Answer: A: K+ 
Explanation: Potassium is the major intracellular cation, it helps to establish resting membrane potential in neurons and nerve fibers after membrane depolarization and action potential Ref:Guyton and Hall textbook of medical physiology 12th edition,page number:50,51,52