The complex [ Fe ( H ₂ O )₅ NO ]²⁺ is formed in the ring test for nitrate ion when freshly prepared FeSO ₄ solution is added to aqueous solution of NO ₃⁻ followed by addition of Conc. H ₂ SO ₄ . This complex is formed by charge transfer in which

Step-by-step solution

aligned Fe ²⁺+ e ⁻ & Fe ⁺ NO & NO ⁺+e⁻ aligned Based on magnetic properties of the complex, it is found that iron has three unpaired electrons thus it exists as Fe ⁺ formed by reduction of Fe ²⁺ by NO which is oxidised to NO ⁺ .