Which of the following complex ions is expected to absorb visible light ? (At. no. Zn =30, Sc =21, Ti =22, Cr =24 )

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Key Idea Only those transition metal complexes are expected to absorb visible light, in which d-subshell is incomplete (ie, has unpaired electron) and excitation of electron from a lower energy arbital to higher energy orbital is possible. (a) In [ Sc ( H ₂ O )₃ ( NH ₃ )₃ ]³⁺, Sc is present as Sc ³⁺ . Sc ³⁺=[ Ar ] 3 ~d ^0, 4 ~s ^0 Since, in this complex excitation of electron is not possible, it will not absorb visible light. (b) In [ Ti ( en )₂ ( NH ₃ )₂ ]⁴⁺, Ti is present as Ti ⁴⁺ . Ti ⁴⁺=[ Ar ] 3 ~d ^0, 4 ~s ^0