Redox Reactions and Electrochemistry: Chemistry | JEE Main
The number of electrons involved in the reduction of permanganate to manganese dioxide in acidic medium is
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Correct answer
The number of electrons involved in the reduction of permanganate (MnO₄⁻) to manganese dioxide (MnO₂) is 3.
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Solution
StepWorking
01given
Permanganate ion is MnO4−. The product is manganese dioxide, MnO2. The medium is acidic.
02find
The number of electrons involved in the reduction half-reaction.
03visualise
Track the oxidation state change of manganese: from MnO4− (where Mn is in +7 state) to MnO2 (where Mn is in +4 state).
04strategise
Write and balance the reduction half-reaction in acidic medium using the ion-electron method: balance Mn, balance O using H2O, balance H using H+, and balance charge using electrons (e−).
05execute
Balancing the half-reaction:
MnO4−+4H++3e−→MnO2+2H2O
Change in oxidation state of Mn: 7−4=3. Hence, 3 electrons are involved.
✓verify
Left-hand side total charge: (−1)+4(+1)+3(−1)=0. Right-hand side total charge: 0. Charges and atoms are completely balanced.
Doesn't MnO4− usually reduce to Mn2+ in acidic medium?
Under standard typical conditions it does, but the stem specifically dictates that the product formed here is MnO2, so we must balance strictly to MnO2.