Answer:
only one oxygen molecule
Explanation:
Hemoglobin (Hb) is an iron-containing oxygen-transport protein localized in vertebrate red blood cells (i.e., erythrocytes). Moreover, the heme group is a component of the Hb protein which is capable of binding or releasing molecular oxygen. Hb consists of four globular protein subunits, and each subunit contains a heme group. This group (heme) binds to an oxygen molecule in a manner that each Hb protein can bind to four oxygen molecules in order to transport them throughout the bloodstream.