Which two transition metal ions has same 3d electronic configuration?
(A) \(Mn^{3+}\)
(B) \(Fe^{2+}\)
(C) \(Mn^{2+}\)
(D) \(Fe^{3+}\)
(E) \(Cr^{3+}\)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (C) and (D) only
To get the 3d configuration of an ion, write the configuration of the neutral atom and remove the 4s electrons first, then 3d electrons.
(A) Mn3+: Mn (Z = 25) is [Ar]3d54s2; removing 4s2 and one 3d electron gives 3d4.
(B) Fe2+: Fe (Z = 26) is [Ar]3d64s2; removing 4s2 gives 3d6.
(C) Mn2+: [Ar]3d54s2 minus 4s2 gives 3d5.
(D) Fe3+: [Ar]3d64s2 minus 4s2 and one 3d electron gives 3d5.
(E) Cr3+: Cr (Z = 24) is [Ar]3d54s1; removing 4s1 and two 3d electrons gives 3d3.
Only \( \ce{Mn^{2+}} \) and \( \ce{Fe^{3+}} \) have the same configuration, the half-filled 3d5: (C) and (D).
Shortcut: ions with the same number of electrons have the same configuration. \( \ce{Mn^{2+}} \) (25 − 2 = 23) and \( \ce{Fe^{3+}} \) (26 − 3 = 23) are isoelectronic.
NCERT (2026-27 edition):
Electronic Configurations – …
