Which of the following complex ions is expected to absorb visible light? (At. nos. Zn = 30, Sc = 21, Ti = 22, Cr = 24)
- [Ti(en)2(NH3)2]4+
- [Cr(NH3)6]3+
- [Zn(NH3)6]2+
- [Sc(H2O)3(NH3)3]3+
Answer
(2) [Cr(NH3)6]3+
Solution
Visible light is absorbed only when a d–d transition is possible (d1 to d9 ions).
Ti4+: 3d0; Zn2+: 3d10; Sc3+: 3d0 no d–d transition, colourless
Cr3+: 3d3 d–d transition possible
[Cr(NH3)6]3+ absorbs visible light.
Answer: (2)