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
A buffer that is most effective at a pH of about 4.5 is: 
Select and explain. 
A. Acetate buffer, B. Bicarbonate buffer, C. Phosphate buffer, D. Tris buffer
A: Acetate buffer
Answer: A: Acetate buffer 
Explanation: A buffer system becomes more effective when the pH of the system equals its pKa. Acetate buffer has a pKa value of 4.76 which nearly equals that of the system. So the buffer that is most effective at a pH of 4.5 is acetate buffer.