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
[{'content': 'Most osmotically active intracellular cation \nSelect and explain. \nA. K+, B. Na+, C. Mg+2, D. Protein', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 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', 'role': 'assistant'}]