Answer:
Attached to hemoglobin.
Step-by-step explanation:
The oxygen is important for the cellular functioning of cell. The carbon dioxide must be move out of the cell and oxygen should reach to each and every cell of the body.
Hemoglobin molecule has the ability to binds with the four molecules of oxygen. The oxygen moves in the body by binding with the hemoglobin molecules present inside the red blood cells.
Thus, the correct answer is option (a).