Which of the following ions will exhibit colour in aqueous solutions?
- La3+ (Z = 57)
- Ti3+ (Z = 22)
- Lu3+ (Z = 71)
- Sc3+ (Z = 21)
Answer
(2) Ti3+ (Z = 22)
Solution
Colour in aqueous solution arises from d–d (or f–f) transitions, which need partly filled d (or f) orbitals.
La3+: [Xe] 4f0; Sc3+: [Ar] 3d0; Lu3+: [Xe] 4f14 empty or completely filled colourless.
Ti3+: [Ar] 3d1 one unpaired d electron d–d transition possible coloured (purple).
Answer: (2)