Question

Which of the following complex ions is expected to absorb visible light?
A. `[Sc(H_(2)O)_(6)]^(3+)`
B. `[Ti(en)_(2)(NH_(3))_(2)]^(4+)`
C. `[Cr(CN)_(6)]^(3-)`
D. `[Co(NH_(3))_(6)]^(3+)`

Answer 1

Correct Answer - 3
In `[Cr(CN)_(5)]^(3-),Cr`is present as `Cr^(3+)`.
`Cr^(3+)=[Ar]3d^(3),4s^(0)`
`[Cr(CN)_(6)]^(3-)=[Ar]`
Since, this complex has three unpaired electrons, excitation of electrons is possible and thus, it is expected that this complex will absorb visible light.