Amongst the following ions which one has the highest magnetic moment value?

(i) [Cr(H₂O)6]³⁺ (ii) [Fe(H₂O)₆]²⁺ (iii) [Zn(H₂O)₆]²⁺

(i) Overall charge balance :

X + 6(0) = + 3

X = + 3.

Cr is in + 3 oxidation state.

Electronic configuration:3d³

As water is a weak field ligand ,it does not call pairing up of the electrons. Number of unpaired electron is equal to 3.

Spin only magnetic moment is given by:

μ = [n(n + 2)]^1/2

μ = [3×5]^1/2

μ = 4BM

(ii) In [Fe(H₂O)₆]³⁺

Electronic configuration of Fe is: [Ar]3d⁶4s²

[Ar] = 1s²2s²2p⁶3s²3p⁶

Electronic configuration of Fe⁺³ = [Ar]3d⁵

Outer electronic configuration of Fe⁺³ = 3d⁵

Overall charge balance:

X + 6(0) = 3

X = + 3

H₂O is weak field ligand so it does not pair the unpaired electron. Total no. of unpaired electron, n = 5.

Spin only magnetic moment is given by:

μ = [n(n + 2)]^1/2

μ = [5×7]^1/2

μ = 5.916BM

(iii) Overall charge balance:

X + 6(0) = + 2

X = + 2

Electronic configuration:3d¹⁰

It has completely filled d orbital, so no. Of unpaired electrons is 0.

μ = 0.

Thus, [Fe(H₂O)₆]³⁺ has highest magnetic moment value.