Question

Explain why Mn²⁺ is more stable than Fe²⁺ towards oxidation to +3 state. (At. no. of Mn = 25, Fe = 26)

Answer 1

1. The electronic configurations of Mn²⁺ are [Ar] 3d⁵ (half‑filled), while Fe²⁺ is [Ar] 3d⁶.
2. A half‑filled 3d⁵ shell is especially stable; removing another electron from Mn²⁺ needs a very high third ionisation enthalpy, so Mn²⁺ resists oxidation.
3. Fe²⁺ is more easily oxidized because Fe³⁺ gives the stable d⁵ state, and the M³⁺/M²⁺ potential for Fe is lower than for Mn.