Q. In which of the following pairs are both the ions coloured in aqueous solution ? (At. no. : Sc = 21, Ti = 22, Ni = 28, Cu = 29, Co = 27)
A) Ni²⁺, Ti³⁺
B) Sc³⁺, Ti³⁺
C) Sc³⁺, Co²⁺
D) Ni²⁺, Cu⁺
Explanation
[Solution from source] Colour needs partly filled d orbitals for d–d transitions. Ni²⁺ (3d⁸) and Ti³⁺ (3d¹) are both coloured. Sc³⁺ is 3d⁰ and Cu⁺ is 3d¹⁰, so each pair containing one of them has a colourless ion. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.