<prompt> One molecule of Hb can bind to a maximum number ofTwo molecules of oxygenOne molecule of oxygenFour molecules of oxygenSix molecules of oxygen  <response>: Hemoglobins bind four molecules of O2 per tetramer, one per heme. A molecule of O2 binds to a hemoglobin tetramer more readily if other O2 molecules are already bound.Reference: Harper;s Biochemistry; 30th edition; Chapter 6; Proteins: Myoglobin Hemoglobin 