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: Biochemistry
HCO3/H2CO3 is the best buffer because it is: 
Select and explain. 
A. pKa near physiological pH, B. Its components can be increased or decreased in the body as needed, C. Good acceptor and donor of H+ ions, D. Combination of a weak acid and weak base
B: Its components can be increased or decreased in the body as needed
Answer: B: Its components can be increased or decreased in the body as needed 
Explanation: Ans: B. Its components can be increased or decreased in the body as needed(Ref:Harper 30/e p11; Gaizung 25/e p6).HCO/H2CO3:Best buffer.As components can be increased or decreased in body as needed.Bicarbonate buffer system:Most powerful extracellular buffer in body.Since both elements of buffer system (HCO 3- & CO).Regulated respectively by kidneys & lungs.pH of extracellular fluid precisely controlled by HCO removal & addition by kidneys & CO 2 removal by lungs.