What is the correct order of following steps in the preparation of potassium permanganate?
(A) disproportionation in a neutral or acidic solution
(B) production of dark green \( K_2MnO_4 \)
(C) \( MnO_2 \)
(D) fusion with alkali metal hydroxide and \( KNO_3 \)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (C), (D), (B), (A)
Potassium permanganate is made from the ore pyrolusite, \( \ce{MnO2} \), in two chemical stages: an oxidative fusion that gives manganate(VI), then a disproportionation of the manganate that gives permanganate(VII).
(C) \( \ce{MnO2} \): the starting material, manganese in the +4 state.
(D) Fusion with alkali metal hydroxide and \( \ce{KNO3} \): \( \ce{MnO2} \) is fused with KOH and an oxidising agent (\( \ce{KNO3} \) or air), which raises Mn to +6.
(B) Production of dark green \( \ce{K2MnO4} \): the fused mass contains potassium manganate, which is dark green.
(A) Disproportionation in a neutral or acidic solution: the manganate ion is unstable there; part of it is oxidised to purple permanganate (+7) and part reduced to \( \ce{MnO2} \) (+4).
Shortcut: The process must start from the ore, \( \ce{MnO2} \), and end with the disproportionation that gives permanganate; only Option (2) starts with (C) and ends with (A).
NCERT (2026-27 edition):
Potassium Permanganate
