Magnetic moment of first series of transition metal complexes is determined by..........
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → spin angular momentum only
A paramagnetic ion owes its magnetic moment to its unpaired electrons, and in principle each electron contributes through its spin angular momentum and its orbital angular momentum. In the compounds of the first transition series, the 3d orbitals are exposed to the surrounding ligands, and the orbital contribution is effectively quenched. The magnetic moment is then decided by the number of unpaired electrons alone and is given by the spin-only formula:
\( \displaystyle \mu = \sqrt{n(n+2)}\ \mathrm{BM} \)
where n is the number of unpaired electrons. For example, \( \ce{Fe^3+} \) (3d5, n = 5) in a high spin complex has \( \mu = \sqrt{35} = 5.92 \) BM.
Why the other options are incorrect
Option (1) subtracting spin angular momentum from orbital angular momentum — Incorrect. The two contributions are never subtracted to give the moment; for these ions the orbital part is quenched altogether.
Option (2) Orbital angular momentum only — Incorrect. This is the part that is quenched, so it contributes almost nothing.
Option (4) product of spin angular momentum and orbital angular momentum — Incorrect. A product would vanish when the orbital part is quenched, yet these ions do have magnetic moments.
NCERT (2026-27 edition):
Magnetic Properties – …
