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
[{'content': 'The major ion in extracellular compartment \nSelect and explain. \nA. K+, B. Na+, C. Cl-, D. HCO3-', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans: b (Na+) Ref: Ganong 22nd ed/ p. 30, 32Most abundant ion in ECF is Na+.ECFMost abundant ion - Na+Most abundant cation - Na+Most abundant anion - Cl-ICF:-Most abundant cation - K+Most abundant anion - PO43- (followed by protein).ECF contains more of Na+, Cl-, HCO3, Ca2+.ICF contains more of K+, PO4, organic anion, protein, magnesium.', 'role': 'assistant'}]