In haemoglobin, iron shows which one of the following oxidation states?

Haemoglobin Iron Oxidation State Explained

This solution explains the oxidation state of iron within the haemoglobin molecule, a vital protein found in red blood cells responsible for transporting oxygen throughout the body.

Role of Iron in Haemoglobin

Haemoglobin contains a special structure called the heme group. At the center of this heme group lies a single atom of iron. This iron atom is the key site where oxygen molecules (O₂) bind to haemoglobin.

Understanding the Oxidation State

The oxidation state refers to the degree of oxidation of an atom in a chemical compound, essentially how many electrons it has lost or gained. For the iron atom within the heme group of functional haemoglobin, the most common and biologically significant oxidation state is the ferrous state.

- The ferrous state corresponds to an oxidation state of +2. This is often represented chemically as ${\text{Fe}}^{2+}$.
- In this ${\text{Fe}}^{2+}$ state, the iron atom can effectively form a reversible coordination bond with an oxygen molecule. This binding allows haemoglobin to pick up oxygen in the lungs and release it in the tissues.

Comparison with Other Oxidation States

While iron can exist in other oxidation states, such as the ferric state (${\text{Fe}}^{3+}$), this is not the primary state for oxygen transport.

- When iron is in the ${\text{Fe}}^{3+}$ state, the resulting molecule is called methemoglobin.
- Methemoglobin is less efficient or unable to bind oxygen properly, highlighting the importance of the ${\text{Fe}}^{2+}$ state for haemoglobin's function.

Analysis of Options

Based on the biological function of haemoglobin:

- Option 1: ${\text{Fe}}^{2+}$ - This is the ferrous state, crucial for oxygen binding.
- Option 2: ${\text{Fe}}^{3+}$ - This is the ferric state, found in methemoglobin, which impairs oxygen transport.
- Option 3: ${\text{Fe}}^{1+}$ - This oxidation state is not typically observed for iron in haemoglobin.
- Option 4: ${\text{Fe}}^{4+}$ - This oxidation state is also not the standard state for iron in haemoglobin's primary oxygen-carrying function.

Therefore, the correct oxidation state of iron in functional haemoglobin is ${\text{Fe}}^{2+}$.