The magnetic nature of elements depends on the presence of unpaired electrons. Identify the configuration of transition elements which shows highest magnetic moment:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \(3d^5\)
The magnetic moment of a first-series transition metal ion is given by the spin-only formula, where n is the number of unpaired electrons:
\( \mu = \sqrt{n(n+2)}\ \text{BM} \)
So the magnetic moment increases with the number of unpaired electrons. Filling the five 3d orbitals by Hund’s rule (singly first, then pairing):
3d7: [↑↓][↑↓][↑][↑][↑] → 3 unpaired; μ = √15 = 3.87 BM
3d5: [↑][↑][↑][↑][↑] → 5 unpaired; μ = √35 = 5.92 BM
3d8: [↑↓][↑↓][↑↓][↑][↑] → 2 unpaired; μ = √8 = 2.83 BM
3d2: [↑][↑][ ][ ][ ] → 2 unpaired; μ = √8 = 2.83 BM
The half-filled 3d5 configuration has the most unpaired electrons and the highest magnetic moment.
Shortcut: five d orbitals can hold at most five unpaired electrons, reached only at d5; no other count can beat it.
NCERT (2026-27 edition):
Magnetic Properties – …
