Question

In aqueous solution, ${Cr}^{2+}$ is a stronger reducing agent than ${Fe}^{2+}$. This is because:

• A. ${Cr}^{2+}$ ion is more stable than ${Fe}^{2+}$.
• B. ${Cr}^{3+}$ ion with $d^3$ configuration has favourable crystal field stabilisation energy.
• C. ${Cr}^{3+}$ has half-filled configuration and hence more stable
• D. ${Fe}^{3+}$ in aqueous solution is more stable than ${Cr}^{3+}$.
• E. ${Fe}^{2+}$ ion with $d^6$ configuration has favourable crystal field stabilisation energy.

Answer 1

The correct option is B ${Cr}^{3+}$ ion with $d^3$ configuration has favourable crystal field stabilisation energy.

$\because {Cr}^{3+}$ ion has $d^3$ configuration $\left(t_{2g}^3{e}_g^0\right)$, which makes ${Cr}^{3+}$ stable by providing crystal field stabilisation energy.
Thus, ${Cr}^{2+}$ ion can easily changes to ${Cr}^{3+}$ (i.e. get oxidised) and acts as a strong reducing agent.
${Cr}^{2+}\to {Cr}^{3+}+e^{-}$