Question:
When MnO$_2$ is fused with KOH and KNO$_2$, a coloured compound is formed. Choose the right compound with the appropriate colour
When MnO$_2$ is fused with KOH and KNO$_2$, a coloured compound is formed. Choose the right compound with the appropriate colour
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Manganate (green) converts to permanganate (purple) on further oxidation.
Updated On: May 1, 2026
- K$_2$MnO$_4$, green
- KMnO$_4$, purple
- Mn$_2$O$_3$, brown
- Mn$_3$O$_4$, black
- MnO$_2$, black
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The Correct Option is A
Solution and Explanation
Concept:
Oxidation of MnO$_2$ in alkaline medium produces manganate ion.
Step 1: Reaction mechanism.
\[ MnO_2 + 2KOH + KNO_2 \rightarrow K_2MnO_4 + NO + H_2O \]
Step 2: Oxidation state change.
Mn: +4 → +6 (oxidation)
Step 3: Colour identification.
• MnO$_4^{2-}$ → green
• MnO$_4^-$ → purple
Step 4: Why others are incorrect.
• (B): KMnO$_4$ formed in further oxidation
• (C), (D), (E): not products of this reaction Final Conclusion:
Green manganate (K$_2$MnO$_4$) is formed.
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