Physiology Excretory System (Kidney, Bladder) Acid-Base Balance ece7e4ef The buffer with the highest pKa is: A Phosphate B Bicarbonate C Intracellular proteins D Ammonia High-Yield Explanation Buffer PKa Phosphate 6.8 Bicarbonate 6.1 Intracellular proteins 7.2 Ammonia 9.0 The only basic buffer is ammonia.