Arrange these transition metal ions, based on decreasing number of unpaired electrons.
A. \(Fe^{2+}\)
B. \(Mn^{2+}\)
C. \(Co^{2+}\)
D. \(Sc^{3+}\)
E. \(Cu^{2+}\)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → B > A > C > E > D
For each ion: take the atom’s configuration, remove the 4s electrons first and then 3d, and fill the five 3d boxes by Hund’s rule.
(B) Mn2+: Mn, Z = 25, [Ar]3d54s2; remove 4s2 → 3d5: [↑][↑][↑][↑][↑] → 5 unpaired.
(A) Fe2+: Fe, Z = 26, [Ar]3d64s2; remove 4s2 → 3d6: [↑↓][↑][↑][↑][↑] → 4 unpaired.
(C) Co2+: Co, Z = 27, [Ar]3d74s2; remove 4s2 → 3d7: [↑↓][↑↓][↑][↑][↑] → 3 unpaired.
(E) Cu2+: Cu, Z = 29, [Ar]3d104s1; remove 4s1 and one 3d → 3d9: [↑↓][↑↓][↑↓][↑↓][↑] → 1 unpaired.
(D) Sc3+: Sc, Z = 21, [Ar]3d14s2; remove 4s2 and 3d1 → 3d0: [ ][ ][ ][ ][ ] → 0 unpaired.
NCERT (2026-27 edition):
Magnetic Properties – …
