Answer: Sc3+ (d0) and Ti4+ (d0) and Zn2+ (d10).
- A Sc3+ (d0) and Ti4+ (d0) and Zn2+ (d10)
- B Fe3+ (d5), which gives pale yellow complexes from a spin-forbidden d-d transition
- C Cu2+ (d9), which gives characteristically blue complexes
- D Ni2+ (d8), which gives characteristically green complexes
Correct answer: A. Sc3+ (d0) and Ti4+ (d0) and Zn2+ (d10)
Explanation: Colourless complexes form with d0 (no d electrons for d-d transitions) and d10 (completely filled, no d-d transitions). Sc3+ and Zn2+ are classic examples.
Aqueous solutions of transition metal ions show characteristic colours caused by electrons absorbing visible light to jump between split d-orbitals; the exact colour depends on the metal, its oxidation state, and surrounding ligands.
Concept context
Transition metals (d-block) and lanthanides/actinides (f-block). Known for coloured compounds, variable oxidation states, complex formation, and catalytic properties. Frequently tested in JEE and NEET.