Answer: Option C.
Haemoglobin binds Hydrogen ion after carbondioxide enters red blood cells.
Explanation:
Haemoglobin is the protein in the red blood cells that help to transport oxygen in the blood. It is an iron compound. Haemoglobin acct as buffer by binding to acid or hydrogen ion in the blood when carbondioxide enters the blood, to remove the acid in the blood before it changes the blood pH.