Which metal ion is present in haemoglobin?

Fe²⁺

The correct answer is option 1.\(Fe^{2+}\).

Haemoglobin is a complex protein found in red blood cells that plays a vital role in transporting oxygen from the lungs to various tissues and organs in the body. The functional unit of haemoglobin is called a heme group, and each heme group contains an iron \((Fe)\) ion in the +2 oxidation state \((Fe^{2+})\).

The iron ion in the heme group can bind to molecular oxygen \((O_2)\) in the lungs, forming oxyhemoglobin. This oxygenated form of hemoglobin travels through the bloodstream, delivering oxygen to tissues where it is needed for cellular respiration. The reversible binding and release of oxygen by haemoglobin are essential for the efficient transport of oxygen throughout the body.

The iron ion undergoes a reversible change in its oxidation state during this oxygen binding and release process, transitioning between \(Fe^{2+}\) (ferrous) and \(Fe^{3+}\) (ferric) states. However, the predominant and biologically active form of iron in haemoglobin is \(Fe^{2+}\).