A buffer that is most effective at a pH of about 4.5 is:
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.
Acetate buffer
Bicarbonate buffer
Phosphate buffer
Tris buffer