Question
Given below are two statements:
Statement-I : Heating NaCl with concentrated $H_2SO_4$ and $MnO_2$ results in oxidation of Mn.
Statement-II : Heating NaI with concentrated $H_2SO_4$ and $MnO_2$ results in reduction of Mn.
In light of the above statements, choose the most appropriate answer from the options given below:
This question was previously asked in
NEET UG Re-Exam 2026 Question Paper (21-Jun-2026)
The correct answer is
Both Statement-I and Statement-II are incorrect.
Analyzing MnO2 Reactions with Halides and Sulfuric Acid
This solution examines the oxidation states of Manganese (Mn) in reactions involving Sodium Chloride (NaCl), Sodium Iodide (NaI), concentrated Sulfuric Acid ($H_2SO_4$), and Manganese Dioxide ($MnO_2$).
Statement I: NaCl with $H_2SO_4$ and $MnO_2$
- Concentrated $H_2SO_4$ reacts with NaCl to generate Hydrogen Chloride ($HCl$).
- $MnO_2$ acts as an oxidizing agent. In the presence of $HCl$, it oxidizes Chloride ($Cl^-$) to Chlorine gas ($Cl_2$).
- The reaction is: $MnO_2 + 4HCl \rightarrow MnCl_2 + Cl_2 + 2H_2O$.
- In this reaction, the oxidation state of Mn changes from $+4$ in $MnO_2$ to $+2$ in $MnCl_2$.
- This represents a reduction of Mn, not an oxidation.
- Therefore, Statement I is incorrect.
Statement II: NaI with $H_2SO_4$ and $MnO_2$
- Concentrated $H_2SO_4$ reacts with NaI. Importantly, concentrated $H_2SO_4$ is a strong oxidizing agent itself.
- $H_2SO_4$ readily oxidizes Iodide ($I^-$) (oxidation state $-1$) to Iodine ($I_2$) (oxidation state $0$). Simultaneously, the sulfur atom in $H_2SO_4$ is reduced from $+6$ to $+4$ (forming $SO_2$).
- The primary reaction driven by the strong oxidizing nature of $H_2SO_4$ on $I^-$ is: $2NaI + 2H_2SO_4 \rightarrow Na_2SO_4 + I_2 + SO_2 + 2H_2O$.
- While $MnO_2$ can act as an oxidizing agent and typically gets reduced by halides in acidic media, the strong oxidizing action of $H_2SO_4$ on $I^-$ dominates this reaction. The reduction of Mn from $MnO_2$ is not the guaranteed primary outcome.
- Statement II claims that Mn is reduced. Since this outcome is uncertain or overshadowed by the reaction between $H_2SO_4$ and $NaI$, the statement is considered incorrect in this context.
Conclusion
Based on the analysis of both statements:
- Statement I is incorrect because Mn is reduced, not oxidized.
- Statement II is incorrect because the reduction of Mn is not the definitive outcome due to the strong oxidizing nature of concentrated $H_2SO_4$ towards $I^-$.
Therefore, both Statement I and Statement II are incorrect.
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