Which gas easily dissolves in the blood but has NO significant role in the body

17.  Hemoglobin

Found in red blood cells, hemoglobin are globular proteins that ferry oxygen (O2) molecules and carbon dioxide (CO2) molecules throughout the body. Each hemoglobin protein structure consists of four polypeptide subunits, which are held together by ionic bonds, hydrogen bonds, hydrophobic interactions, and van der Waals forces, as well as four heme pigments, one in each of the subunits.  These heme groups contain positively-charged iron (Fe2+) molecules which can reversibly bind to oxygen molecules and transport them to various areas of the body. As the heme groups bind or release their oxygen loads, the overall hemoglobin undergoes conformational changes which alters their affinity for oxygen.

Could it be nitrogen? CO2 has an effect, CO has an effect, so the only one I can think of is N2.