Question

In the following Latimer diagram, the species that undergoes disproportionation reaction is
\[ \text{MnO}_4^- \xrightarrow{+0.56} \text{MnO}_4^{2-} \xrightarrow{+0.27} \text{MnO}_3^- \xrightarrow{+0.93} \text{MnO}_2 \xrightarrow{+0.15} \text{Mn}_2\text{O}_3 \xrightarrow{-0.25} \text{Mn(OH)}_2 \xrightarrow{-1.56} \text{Mn} \]

• A. MnO$_4^{2-}$
• B. MnO$_3^{-}$
• C. Mn$_2$O$_3$
• D. Mn(OH)$_2$

Hint:

In Latimer diagrams, a species disproportionates if E(left)<E(right).

Answer 1

The Correct Option is B

Step 1: Condition for disproportionation.
A species will undergo disproportionation if its reduction potential (left) is more positive than its oxidation potential (right). That is:
E(left)>E(right).
Step 2: Applying to MnO$_3^-$.
For MnO$_3^-$: Left potential = +0.27
Right potential = +0.93
Since the right value is greater, oxidation is favored, meaning the species is unstable and tends to disproportionate.
Step 3: Conclusion.
MnO$_3^-$ satisfies the condition for disproportionation.