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+

The magnetic moment of a complex ion is determined by the number of unpaired electrons in the d-orbitals of the central metal ion. The more unpaired electrons, the higher the magnetic moment.

(i) [Cr(H2O)6]3+: Chromium in this complex is in the +3 oxidation state. The electronic configuration of Cr is [Ar] 3d5 4s1. In the +3 oxidation state, it becomes [Ar] 3d3. Therefore, there are 3 unpaired electrons.

(ii) [Fe(H2O)6]2+: Iron in this complex is in the +2 oxidation state. The electronic configuration of Fe is [Ar] 3d6 4s2. In the +2 oxidation state, it becomes [Ar] 3d6. Therefore, there are 4 unpaired electrons.

(iii) [Zn(H2O)6]2+: Zinc in this complex is in the +2 oxidation state. The electronic configuration of Zn is [Ar] 3d10 4s2. In the +2 oxidation state, it becomes [Ar] 3d10. Therefore, there are no unpaired electrons.

So, [Fe(H2O)6]2+ has the highest magnetic moment value because it has the most unpaired electrons.