In cellular respiration, animals use oxygen (O2) to harvest energy from their food, giving off carbon dioxide (CO2) as a waste product. To maintain their metabolism, animals' circulatory and respiratory systems keep O2 flowing to body tissues and remove CO2 to prevent the poisoning of cells. Almost all vertebrates use a respiratory pigment called hemoglobin to aid in this process.

Hemoglobin is a metalloprotein that lead oxygen to reach our cells

Explanation:

As you can see in the image bellow, hemoglobin is a protein inside our red blood cells, which is rich in iron that allows oxygen to be transported through our blood until the cells and get back CO2 to our lungs, where the exchange takes place.

the atomic number will stay the same no matter how many electrons it has, so it doesn’t decrease nor increase. it’ll only change with a different number of protons