Statement I: The Fe2+ ion is more stable than the Fe3+ ion.
Statement II: The Fe3+ ion has a half-filled 3d subshell.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Statement I is incorrect but Statement II is correct
Configuration of Fe: Fe (Z = 26) is [Ar]3d64s2.
\( \ce{Fe^2+} \): the two 4s electrons are removed, giving 3d6.
\( \ce{Fe^3+} \): one more 3d electron is removed, giving 3d5, with one electron in each of the five 3d orbitals.
Statement I: The Fe2+ ion is more stable than the Fe3+ ion. — False. The comparatively low E°(Fe3+/Fe2+) value shows the extra stability of Fe3+; \( \ce{Fe^2+} \) (d6) is the less stable of the two ions.
Statement II: The Fe3+ ion has a half-filled 3d subshell. — True. 3d5 is a half-filled 3d subshell.
NCERT (2026-27 edition):
4.3.6 Trends in the M3+/M2+ Standard Electrode Potentials – “… The comparatively high value for Mn shows that Mn2+(d5) is particularly stable, whereas comparatively low value for Fe shows the extra stability of Fe3+ (d5).”