Iron atom in the Haemoglobin of blood is in the +2 Oxidation state. ie., Iron is present as Fe(II) ion. If it is present in the +3 Oxidation state, then it cannot coordinate with the oxygen atom. The oxidation state of Fe in Hemoglobin is +2.

Oxidation State of Iron in Haemoglobin

Haemoglobin is a protein found in red blood cells that is responsible for transporting oxygen throughout the body. It consists of four subunits, each containing a heme group, which is a complex of iron and a porphyrin molecule. The iron in haemoglobin is essential for its function in binding and releasing oxygen.

1. Structure of Haemoglobin
- Haemoglobin is a globular protein composed of long chains of amino acids that are folded into a compact shape.
- It consists of four subunits, each containing a heme group.
- The heme group is located in a pocket within each subunit, where it binds to oxygen.

2. Heme Group
- The heme group is a complex of iron and a porphyrin molecule.
- The porphyrin molecule consists of a planar ring structure with nitrogen atoms at the corners, forming a coordination complex with iron in the center.
- The iron in the heme group can exist in different oxidation states, including Fe2+ and Fe3+.

3. Oxidation State of Iron in Haemoglobin
- In its oxygenated state, the iron in haemoglobin exists in the +2 oxidation state (Fe2+).
- When oxygen binds to the iron atom, it forms a coordination bond, resulting in the formation of oxyhaemoglobin.
- In this state, the iron is coordinated to the oxygen molecule, stabilizing the oxygen and allowing it to be transported throughout the body.

4. Oxygen Binding and Release
- When haemoglobin comes into contact with oxygen in the lungs, the iron in the heme group undergoes a change in oxidation state from Fe2+ to Fe3+.
- This change in oxidation state facilitates the binding of oxygen to the iron atom, forming oxyhaemoglobin.
- Oxyhaemoglobin then travels through the bloodstream, delivering oxygen to tissues and organs throughout the body.
- In the tissues, oxyhaemoglobin releases oxygen, and the iron atom returns to its Fe2+ oxidation state.

Conclusion
The oxidation state of iron in haemoglobin is Fe2+. This allows the iron to bind and release oxygen, enabling haemoglobin to perform its crucial role in oxygen transport.