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
[{'content': 'The most abundant extracellular cation is? \nSelect and explain. \nA. Chloride, B. Sodium, C. Calcium, D. Potassium', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Potassium is the most abundant cation in intracellular fluid.\nPhosphate is the most abundant intracellular anion.\nSodium is the most abundant extracellular cation.\nChloride is the most abundant extracellular anion.', 'role': 'assistant'}]