Chemistry - Coordination Chemistry Question with Solution | TestHub

For a complex ion to absorb light in the visible region, it must undergo d-d transitions or charge-transfer transitions.

A. In $[Ti(en{)}_3{]}^{4+}$, Ti is in the +4 oxidation state ($d^0$ configuration). No d-d transitions are possible.

B. In $[Sc(N{H}_3{)}_4(H_{2}O{)}_2{]}^{3+}$, Sc is in the +3 oxidation state ($d^0$ configuration). No d-d transitions are possible.

C. In $[Cr{O}_4{]}^{2-}$, Cr is in the +6 oxidation state ($d^0$ configuration). However, it exhibits ligand-to-metal charge transfer (LMCT) transitions, which absorb visible light.

D. In $[Zn(CN{)}_4{]}^{2-}$, Zn is in the +2 oxidation state ($d^{10}$ configuration). No d-d transitions are possible.

Therefore, $[Cr{O}_4{]}^{2-}$ is expected to absorb light in the visible region due to LMCT.

The final answer is $\boxed{C}$