Q9 / 180 · COMEDK 2023 (Morning Shift) · Chemistry
In dilute alkaline solution $\mathrm{MnO}_4^{-}$ changes to
- A$\mathrm{Mn}_2 \mathrm{O}_3$
- B$\mathrm{MnO}$
- C$\mathrm{MnO}_4^{2-}$
- Correct answerD$\mathrm{MnO}_2$
Solution
In a dilute alkaline or neutral medium, the permanganate ion $\mathrm{MnO}_{4}^{-}$ acts as an oxidizing agent and undergoes reduction to form manganese dioxide, $\mathrm{MnO}_{2}$.
The balanced chemical equation for this reduction is:
$2\mathrm{MnO}_{4}^{-} + \mathrm{H}_{2}\mathrm{O} + 3e^{-} \rightarrow 2\mathrm{MnO}_{2} + 2\mathrm{OH}^{-}$
In this reaction, the oxidation state of manganese changes from $+7$ in $\mathrm{MnO}_{4}^{-}$ to $+4$ in $\mathrm{MnO}_{2}$.
Answer: $\mathrm{MnO}_2$
The balanced chemical equation for this reduction is:
$2\mathrm{MnO}_{4}^{-} + \mathrm{H}_{2}\mathrm{O} + 3e^{-} \rightarrow 2\mathrm{MnO}_{2} + 2\mathrm{OH}^{-}$
In this reaction, the oxidation state of manganese changes from $+7$ in $\mathrm{MnO}_{4}^{-}$ to $+4$ in $\mathrm{MnO}_{2}$.
Answer: $\mathrm{MnO}_2$
Hence, the correct answer is option: 'D'.