Question

Why is the Zn²⁺ ion colourless?

Answer 1

1. Zn²⁺ ions have a completely filled d-orbital configuration (3d¹⁰).
2. Colour in transition metal ions arises from d-d electronic transitions involving unpaired electrons.
3. Because Zn²⁺ has no unpaired electrons, no d-d transitions can occur.
4. Without d-d transitions, Zn²⁺ does not absorb visible light and thus appears colourless.
5. Similar behaviour is observed in ions like Cu⁺, Cd²⁺, and Hg^2+, which also have filled d-orbitals.

Hence, Zn²⁺ ions are colourless due to a lack of unpaired d-electrons and no d-d electronic transitions.