Answer:
H+
Step-by-step explanation:
Hemoglobin is the major protein of red blood cells. It has many exposed amino groups and carboxylic groups at its surface. These NH3 and COOH groups serve as weak acids and bases respectively and allow hemoglobin to serve as a buffer to maintain the pH of the RBC cytoplasm.
As the exposed amino groups of hemoglobin protein bind to the H+ ions, the free H+ concentration of the cytoplasm of RBC is reduced leading to a buffer action to maintain the pH.