Question

Given below are two statements:
Statement-I : Heating NaCl with concentrated $\text{H}_2\text{SO}_4$ and $\text{MnO}_2$ results in oxidation of Mn.
Statement-II : Heating NaI with concentrated $\text{H}_2\text{SO}_4$ and $\text{MnO}_2$ results in reduction of Mn.
In light of the above statements, choose the most appropriate answer from the options given below:

• A. Statement-I is incorrect but Statement-II is correct
• B. Both Statement-I and Statement-II are correct
• C. Both Statement-I and Statement-II are incorrect
• D. Statement-I is correct but Statement-II is incorrect

Hint:

To avoid confusion with redox terminology: - An oxidizing agent (like $\text{MnO}_2$) oxidizes other species while always undergoing reduction itself. - Consequently, in any successful oxidation reaction driven by $\text{MnO}_2$, the manganese ion will always be reduced from $\text{Mn}^{+4}$ to $\text{Mn}^{+2}$.

Answer 1

The Correct Option is A

Step 1: Know the role of MnO2 here.
In both statements \(MnO_2\) is heated with a sodium halide and concentrated \(H_2SO_4\). \(MnO_2\) acts as the oxidising agent, so it takes electrons and is itself reduced.
Step 2: Track manganese in general.
In \(MnO_2\) manganese is \(+4\). After reaction it ends up in \(MnSO_4\), where manganese is \(+2\). Going from \(+4\) to \(+2\) means manganese is reduced in either case.
Step 3: Analyse Statement-I (NaCl).
\[ 2NaCl + MnO_2 + 3H_2SO_4 \rightarrow 2NaHSO_4 + MnSO_4 + Cl_2 + 2H_2O \] Here \(Cl^-\) is oxidised to \(Cl_2\), while Mn drops from \(+4\) to \(+2\), so Mn is reduced, not oxidised. Statement-I claims oxidation of Mn, so it is incorrect.
Step 4: Analyse Statement-II (NaI).
\[ 2NaI + MnO_2 + 3H_2SO_4 \rightarrow 2NaHSO_4 + MnSO_4 + I_2 + 2H_2O \] Again Mn falls from \(+4\) to \(+2\), so Mn is reduced. Statement-II claims reduction of Mn, which is correct.
Step 5: Compare the two verdicts.
Statement-I is wrong and Statement-II is right.
Step 6: Pick the option.
This matches option 1.
\[ \boxed{\text{Statement-I is incorrect but Statement-II is correct}} \]