Single correct · +4 / −1
The deep purple colour of KMnO₄ is due to:
- (a) d-d transition
- (b) Charge transfer from O to Mn
- (c) f-f transition
- (d) Paramagnetism
Answer and solution
Answer (b) Charge transfer from O to Mn
Solution
Chemistry ma’am · 4 steps
Mn in permanganate is +7, so it has no d electrons at all: the colour has to come from somewhere else.
- Find the d count. In MnO₄⁻, Mn is in the +7 state. Mn is [Ar] 3d⁵ 4s², so losing 7 electrons leaves 3d⁰.
- No d-d possible. A d-d transition needs at least one d electron to jump between d orbitals. With 3d⁰ there is nothing to excite, so d-d cannot explain the colour.
- Charge transfer. Instead, visible light moves an electron from a filled orbital on the oxide ligand (O²⁻) into an empty orbital on Mn⁷⁺. This ligand-to-metal charge transfer is fully allowed, so it absorbs very strongly and gives the intense purple.
- So. The deep purple colour of KMnO₄ is due to charge transfer from O to Mn, option (b).
The idea to keep. Intense colour with a d⁰ metal, like MnO₄⁻ or Cr₂O₇²⁻, always means ligand-to-metal charge transfer. First find the d electron count; zero rules out d-d.
Answer from the NTA final answer key. Solution by PrepWiser.