### Related Formula textIE propto frac1textStability of electronic configuration$\text{IE} \propto \frac{1}{\text{Stability of electronic configuration}}$ ### Core Logic Let's examine the configurations: - For Mn^2+$Mn^{2+}$, the electronic configuration is [Ar]3d^5$[Ar]3d^5$, which features a highly stable, symmetric half-filled d-subshell. - For Fe^2+$Fe^{2+}$, the configuration is [Ar]3d^6$[Ar]3d^6$. Because of the extra exchange energy and stability of the half-filled 3d^5$3d^5$ state, it is harder to remove an electron from Mn^2+$Mn^{2+}$ than from Fe^2+$Fe^{2+}$. Therefore, the ionisation enthalpy of Mn^2+$Mn^{2+}$ is greater than that of Fe^2+$Fe^{2+}$: textIE(Mn^2+) > textIE(Fe^2+)$\text{IE}(Mn^{2+}) > \text{IE}(Fe^{2+})$ Hence, the expression Mn^2+ < Fe^2+$Mn^{2+} < Fe^{2+}$ is incorrect. ### Pattern Recognition Whenever you see manganese (Mn$Mn$) in the +2$+2$ oxidation state, remember its exceptionally stable d^5$d^5$ config. This creates anomalous spikes in successive ionisation energies compared to neighboring iron (Fe$Fe$). ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Chemistry: The d and f Block Elements