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
The most abundant extracellular cation is? 
Select and explain. 
A. Chloride, B. Sodium, C. Calcium, D. Potassium
B: Sodium
Answer: B: Sodium 
Explanation: Potassium is the most abundant cation in intracellular fluid.
Phosphate is the most abundant intracellular anion.
Sodium is the most abundant extracellular cation.
Chloride is the most abundant extracellular anion.