In neutral or mild alkaline solutions, potassium permanganate oxidizes manganous salt ($Mn^{2+}$) to.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → $MnO_2$
Potassium permanganate (KMnO₄) is a strong oxidizing agent, but its oxidizing behaviour depends on the medium in which the reaction takes place.
The reduction product of permanganate ion MnO₄⁻ varies as follows:
In acidic medium MnO₄⁻ is reduced to Mn²⁺
In neutral or mildly alkaline medium MnO₄⁻ is reduced to MnO₂
In strongly alkaline medium MnO₄⁻ is reduced to MnO₄²⁻ (manganate ion)
Since the question specifies neutral or mildly alkaline solution, MnO₄⁻ will be reduced to MnO₂. During this process, KMnO₄ acts as an oxidizing agent and oxidizes Mn²⁺ (manganous ion) to MnO₂.
Oxidation state change of manganese: Mn²⁺ → MnO₂
In Mn²⁺, oxidation state of Mn = +2
In MnO₂, oxidation state of Mn = +4
Thus, Mn²⁺ undergoes oxidation.
Relevant half reactions in neutral/mild alkaline medium:
Reduction of permanganate:
MnO₄⁻ + 2H₂O + 3e⁻ → MnO₂ + 4OH⁻
Oxidation of manganous ion:
Mn²⁺ + 2H₂O → MnO₂ + 4H⁺ + 2e⁻
Overall, manganous ion is oxidized to MnO₂, which appears as a brown precipitate.
Why other options are incorrect:
Option 2 Mn²⁺
No oxidation occurs. This is the starting species.
Option 3 MnO₄²⁻
This forms only in strongly alkaline medium, not in neutral or mildly alkaline medium.
Option 4 MnO₄⁻
This is permanganate itself, not the oxidation product of Mn²⁺.