Question

The following reaction can be best described as: \[ 3\mathrm{MnO_4^{2-}}+4\mathrm{H^+} \rightarrow 2\mathrm{MnO_4^-} +\mathrm{MnO_2} +2\mathrm{H_2O} \]

• A. Coupling
• B. Disproportionation
• C. Displacement
• D. Oxidative fusion

Hint:

Whenever the same oxidation state appears on the reactant side and produces both higher and lower oxidation states on the product side, think of disproportionation.

Answer 1

The Correct Option is B

Step 1: Determine oxidation state of Mn in manganate ion.
For \[ \mathrm{MnO_4^{2-}} \] let oxidation state of Mn be \(x\). \[ x+4(-2)=-2 \] \[ x=+6 \]

Step 2: Determine oxidation states in the products.
For \[ \mathrm{MnO_4^-} \] \[ x+4(-2)=-1 \] \[ x=+7 \] For \[ \mathrm{MnO_2} \] \[ x+2(-2)=0 \] \[ x=+4 \]

Step 3: Analyse oxidation and reduction.
One part of Mn(+6) is oxidised to Mn(+7). Another part of Mn(+6) is reduced to Mn(+4). Thus the same species undergoes both oxidation and reduction.

Step 4: Identify the reaction type.
Hence the reaction is a disproportionation reaction. \[ {\text{Disproportionation}} \]