Standard Electrode Potential Anomaly

The unusually high positive reduction potential of the Mn^3+/Mn^2+ couple reflects the special stability gained on reduction. Manganese(III) has the configuration 3d^4, while manganese(II) has the configuration 3d^5, an exactly half-filled d-subshell that is especially stable because of its symmetrical electron distribution and favourable exchange energy. The strong drive to reach this stable half-filled configuration makes Mn^3+ readily accept an electron to become Mn^2+, giving a large positive reduction potential and making Mn^3+ a strong oxidising agent. The option that Mn^2+ has an unstable configuration is the opposite of the truth. The option that Mn^3+ is already very stable contradicts its tendency to be reduced. The option that manganese has no d-electrons is false. This thermodynamic anomaly tied to half-filled stability is a key JEE Advanced concept. Such questions reward conceptual clarity, since a student who truly grasps electrode potential anomaly can solve many superficially different variants with the same approach. Examiners frequently test whether a student can connect Mn3+/Mn2+ couple with the underlying principle rather than merely recalling an isolated fact. Plausibility check: the strong oxidising behaviour of Mn^3+, which disproportionates readily to Mn^2+ and MnO_2, confirms the driving force toward the stable 3d^5 configuration.