Which one of the following metal ions will exhibit highest value of c…

The correct answer is Option (2) → Cr²⁺

The spin-only magnetic moment depends only on the number of unpaired electrons (n):

    \( \displaystyle \mu=\sqrt{n(n+2)}\ \text{BM} \)

The more unpaired electrons, the larger the moment. When a first-row metal forms an ion, the 4s electrons are removed first, then the 3d electrons.

Cr (Z = 24) is [Ar]3d⁵4s¹; losing the 4s electron and one 3d electron gives Cr²⁺: 3d⁴, with 4 unpaired electrons, μ = √24 = 4.90 BM.

So Cr²⁺, with four unpaired electrons, has the highest spin-only magnetic moment.

Why the other options are incorrect

• Option (1) Co²⁺ — Incorrect. Co (Z = 27) is [Ar]3d⁷4s²; losing the two 4s electrons gives 3d⁷: 3 unpaired electrons, μ = √15 = 3.87 BM.

• Option (3) Cu²⁺ — Incorrect. Cu (Z = 29) is [Ar]3d¹⁰4s¹; losing the 4s electron and one 3d electron gives 3d⁹: only 1 unpaired electron, μ = √3 = 1.73 BM.

• Option (4) Ti²⁺ — Incorrect. Ti (Z = 22) is [Ar]3d²4s²; losing the two 4s electrons gives 3d²: 2 unpaired electrons, μ = √8 = 2.83 BM.

NCERT (2026-27 edition):
Magnetic Properties – …