Question

The violet colour of \(KMnO_4\) solution is due to:

• A. \(d-d\) transition
• B. Charge transfer transition
• C. Presence of unpaired electrons
• D. Hybridization

Hint:

Compounds having \(d^0\) or \(d^{10}\) configuration generally do not show \(d-d\) transitions. Their colour usually arises from charge transfer transitions.

Answer 1

The Correct Option is B

Concept: Colour in transition metal compounds may arise due to:
• \(d-d\) transitions
• Charge transfer transitions In permanganate ion: \[ MnO_4^- \] manganese exists in: \[ +7 \] oxidation state.

Step 1: Find electronic configuration of manganese.
Atomic number of manganese: \[ 25 \] Electronic configuration: \[ Mn=[Ar]\,3d^5 4s^2 \] For: \[ Mn^{7+} \] all seven valence electrons are removed. Thus: \[ Mn^{7+}=[Ar]\,3d^0 \] There are no electrons in \(d\)-orbitals.

Step 2: Check possibility of \(d-d\) transition.
For \(d-d\) transition:
• Electrons must be present in \(d\)-orbitals. But: \[ Mn^{7+}=3d^0 \] Therefore: \[ d-d \] transition is impossible.

Step 3: Identify actual reason for violet colour.
In permanganate ion:
• Electrons transfer from oxygen ligand orbitals to empty metal orbitals. This process is known as: \[ \text{Charge transfer transition} \] Charge transfer transitions are usually very intense, which explains the deep violet colour of: \[ KMnO_4 \] Hence, the correct answer is: \[ \boxed{\text{Charge transfer transition}} \]