Question

The correct order of increasing intensity (molar absorptivity) of the UV-visible absorption bands for the ions [Ti(H\(_2\)O)\(_6\)]\(^{3+}\), [Mn(H\(_2\)O)\(_6\)]\(^{2+}\), [CrO\(_4\)]\(^{2-}\), and [NiCl\(_4\)]\(^{2-}\) is:

• A. [Ti(H\(_2\)O)\(_6\)]\(^{3+}\) < [Mn(H\(_2\)O)\(_6\)]\(^{2+}\) < [CrO\(_4\)]\(^{2-}\) < [NiCl\(_4\)]\(^{2-}\)
• B. [Mn(H\(_2\)O)\(_6\)]\(^{2+}\) < [Ti(H\(_2\)O)\(_6\)]\(^{3+}\) < [NiCl\(_4\)]\(^{2-}\) < [CrO\(_4\)]\(^{2-}\)
• C. [NiCl\(_4\)]\(^{2-}\) < [Ti(H\(_2\)O)\(_6\)]\(^{3+}\) < [Mn(H\(_2\)O)\(_6\)]\(^{2+}\) < [CrO\(_4\)]\(^{2-}\)
• D. [Ti(H\(_2\)O)\(_6\)]\(^{3+}\) < [NiCl\(_4\)]\(^{2-}\) < [CrO\(_4\)]\(^{2-}\) < [Mn(H\(_2\)O)\(_6\)]\(^{2+}\)

Hint:

The UV-visible absorptivity depends on the charge and coordination of the metal ion, with higher charge density leading to stronger absorption.

Answer 1

The Correct Option is B

The intensity of UV-visible absorption bands is related to the electronic transitions in metal ions. The molar absorptivity increases with the ability of the metal ion to absorb light, which in turn depends on the electronic structure and the presence of ligands. - The \( Ti^{3+} \) ion has a lower charge density than \( Cr^{2-} \), making it absorb less strongly.
- \( Mn^{2+} \), with a d\(^5\) configuration, has relatively weak absorption bands compared to others.
- \( CrO_4^{2-} \), being an anion with a high charge density, has the highest absorptivity.
Thus, the correct order is: \[ \text{[Mn(H}_2\text{O)}_6]^{2+} < \text{[Ti(H}_2\text{O)}_6]^{3+} < \text{[NiCl}_4]^{2-} < \text{[CrO}_4]^{2-}. \] Final Answer: (B) [Mn(H\(_2\)O)\(_6\)]\(^{2+}\) < [Ti(H\(_2\)O)\(_6\)]\(^{3+}\) < [NiCl\(_4\)]\(^{2-}\) < [CrO\(_4\)]\(^{2-}\).