According to the chemical reac- tion, if there are 4.5 mol of oxy- genated hemoglobin present in an excess of carbon monoxide, how many moles of hemoglobin would release oxygen and bind to carbon monoxide?

A single molecule of hemoglobin can bind to 4 molecules of oxygen gas. However, hemoglobin has a greater affinity for carbon monoxide than oxygen. Therefore, an excess of carbon monoxide in the presence of oxygenated hemoglobin will result in the displacement of each oxygen atom for a carbon monoxide atom.

Hb(O2)4 (aq) + 4 CO(g) --> Hb(CO)4 (aq) + 4 O2(g)

With an excess of carbon monoxide, it is safe to assume that each oxygen molecule will be displaced with a carbon monoxide molecule. Therefore, if we have 4.5 moles of oxygenated hemoglobin (Hb(O2)4), all 4.5 moles of the species will release oxygen and bind to carbon monoxide. 

This scenario is called diffusion. particles are moving from regions of high concentration to low concentration.