The intense deep purple color of Potassium Permanganate ($KMnO_4$) is attributed to which of the following?

The intense deep purple color of Potassium Permanganate (KMnO₄) is attributed to which of the following? +

Correct Answer

Ligand-to-Metal Charge Transfer (LMCT) from O²⁻ to Mn⁷⁺.

Detailed Explanation

In potassium permanganate:

KMnO₄ → K⁺ + MnO₄⁻

The oxidation state of manganese is:

+1 + x + 4(−2) = 0
x = +7

Thus, manganese is present in the very high +7 oxidation state. Mn⁷⁺ has a d⁰ configuration. Therefore, the intense purple colour is not due to ordinary d–d transitions. Instead, when light falls on MnO₄⁻, an electron can be transferred from an oxygen-based orbital to a manganese-based orbital:

O → Mn charge-transfer transition

This is called a Ligand-to-Metal Charge Transfer (LMCT) transition. Because charge-transfer transitions are highly allowed, they absorb strongly in the visible region, producing the characteristic intense deep-purple colour.

Why Not d–d Transition?

A common competitive-exam trap is to say that the purple colour is caused by a d–d transition. This is incorrect. Mn in MnO₄⁻ is:

Mn⁷⁺ = d⁰

Since there are no d-electrons, a conventional d–d transition cannot occur. Therefore:

Deep purple colour → LMCT, not d–d transition

JEE / NEET Quick Trick

d⁰ or d¹⁰ species can still be coloured due to charge-transfer transitions.

KMnO₄: Mn⁷⁺ → d⁰ → LMCT → Purple

30 Related MCQs with Solutions

1. The intense purple colour of KMnO₄ is due to:

A. d–d transition

B. Ligand-to-metal charge transfer

C. Metal-to-ligand charge transfer

D. f–f transition

Answer: B. Ligand-to-metal charge transfer (LMCT)

2. Oxidation state of Mn in MnO₄⁻ is:

A. +2

B. +4

C. +6

D. +7

Answer: D. +7

3. The d-electron configuration of Mn⁷⁺ is:

A. d⁰

B. d²

C. d⁵

D. d¹⁰

Answer: A. d⁰

4. Can MnO₄⁻ show a normal d–d transition?

A. Yes

B. No

C. Only in solid state

D. Only at high pressure

Answer: B. No
Mn⁷⁺ is d⁰.

5. LMCT means:

A. Ligand-to-Metal Charge Transfer

B. Ligand-Metal Crystal Transition

C. Light-Metal Charge Transfer

D. Lone-pair Metal Transfer

Answer: A

6. In LMCT of permanganate, electron density moves mainly:

A. Mn → O

B. O → Mn

C. K → O

D. K → Mn

Answer: B. O → Mn

7. Which ion is responsible for the purple colour of KMnO₄?

A. K⁺

B. Mn²⁺

C. MnO₄⁻

D. O²⁻

Answer: C. MnO₄⁻

8. Which transition is generally intense?

A. Spin-forbidden d–d

B. Charge-transfer transition

C. Nuclear transition

D. Rotational transition

Answer: B. Charge-transfer transition

9. The colour of permanganate ion is:

A. Deep purple

B. Green

C. Yellow

D. Colourless

Answer: A. Deep purple

10. Which statement is correct?

A. MnO₄⁻ is coloured because Mn⁷⁺ has many d-electrons

B. MnO₄⁻ is coloured due to charge transfer

C. KMnO₄ is coloured due to K⁺

D. MnO₄⁻ has an f–f transition

Answer: B

11. MnO₄⁻ contains manganese in:

A. +2 oxidation state

B. +3 oxidation state

C. +6 oxidation state

D. +7 oxidation state

Answer: D

12. Mn⁷⁺ has how many d-electrons?

A. 0

B. 2

C. 5

D. 7

Answer: A. 0

13. A d⁰ complex can be coloured mainly because of:

A. d–d transitions

B. Charge-transfer transitions

C. f–f transitions

D. Nuclear decay

Answer: B

14. Which orbital is mainly the electron donor in LMCT of permanganate?

A. Oxygen-based orbital

B. Potassium orbital

C. Hydrogen orbital

D. Chlorine orbital

Answer: A. Oxygen-based orbital

15. Which is NOT responsible for the purple colour of MnO₄⁻?

A. Charge transfer

B. O → Mn electron transfer

C. Conventional d–d transition

D. Absorption of visible light

Answer: C

16. The charge on permanganate ion is:

A. +1

B. −1

C. −2

D. +2

Answer: B. −1

17. KMnO₄ contains:

A. K²⁺ and MnO₄⁻

B. K⁺ and MnO₄⁻

C. K⁺ and MnO₄²⁻

D. K²⁺ and MnO₄²⁻

Answer: B

18. Charge-transfer bands are usually:

A. Very weak

B. Relatively intense

C. Always invisible

D. Nuclear in origin

Answer: B. Relatively intense

19. Which ion is commonly cited as a d⁰ coloured species?

A. MnO₄⁻

B. Zn²⁺

C. Sc³⁺

D. Ca²⁺

Answer: A. MnO₄⁻

20. Why is KMnO₄ a strong oxidising agent?

A. Mn is in a high +7 oxidation state

B. K is a noble gas

C. It has d¹⁰ Mn

D. It contains no oxygen

Answer: A

21. Which statement about MnO₄⁻ is correct?

A. It is d⁵

B. It is d⁰

C. It is d¹⁰

D. It is f⁷

Answer: B. d⁰

22. The purple colour results from absorption of:

A. Visible light

B. Only radio waves

C. Only microwaves

D. Only X-rays

Answer: A. Visible light

23. Which is the best explanation of the colour?

A. Mn⁷⁺ undergoes d–d transition

B. Electron transfer from O to Mn occurs upon light absorption

C. K⁺ absorbs visible light strongly

D. Mn has 10 d-electrons

Answer: B

24. Which oxidation state corresponds to d⁰ manganese?

A. +2

B. +4

C. +6

D. +7

Answer: D. +7

25. The ligand in permanganate responsible for LMCT is:

A. O

B. K

C. Mn

D. None

Answer: A. Oxygen

26. Which type of transition is generally much more intense than a d–d transition?

A. Charge-transfer transition

B. Spin transition only

C. Nuclear transition

D. Vibrational transition

Answer: A

27. In LMCT, the electron moves:

A. From ligand to metal

B. From metal to ligand

C. From K to O

D. From nucleus to ligand

Answer: A

28. Which species is responsible for the characteristic colour of permanganate solutions?

A. K⁺

B. MnO₄⁻

C. H₂O

D. Mn metal

Answer: B

29. The oxidation state of Mn in KMnO₄ is:

A. +2

B. +4

C. +6

D. +7

Answer: D. +7

30. The correct match is:

A. KMnO₄ — d–d transition

B. KMnO₄ — LMCT — deep purple

C. KMnO₄ — f–f transition

D. KMnO₄ — K⁺ transition

Answer: B. LMCT — deep purple

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