Why is Fe³⁺ more stable than Fe²⁺?
Correct answer C. Fe³⁺ has a half-filled 3d⁵ subshell
Explanation
Fe²⁺ is 3d⁶, whereas Fe³⁺ is 3d⁵. The symmetrical half-filled d subshell has extra exchange energy, which is why Fe²⁺ is readily oxidised to Fe³⁺.
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