Question

Identify the correct coefficients (a), (b), (c) and (d) in the following equations
\[ \text{i) } xMnO_4^- + (a)\,SO_3^{2-} + (b)\,H^+ \rightarrow xMn^{2+} + (a)\,SO_4^{2-} + (c)\,H_2O \]
\[ \text{ii) } (c)\,S_2O_3^{2-} + (d)\,MnO_4^- + H_2O \rightarrow (d)\,MnO_2 + (b)\,SO_4^{2-} + xOH^- \]

• A. \( (a)=3,\,(b)=8,\,(c)=6,\,(d)=6 \)
• B. \( (a)=5,\,(b)=6,\,(c)=3,\,(d)=8 \)
• C. \( (a)=2,\,(b)=8,\,(c)=4,\,(d)=4 \)
• D. \( (a)=2,\,(b)=6,\,(c)=6,\,(d)=5 \)

Hint:

Always identify medium (acidic/basic) before balancing redox reactionsPermanganate behaves differently in different media.

Answer 1

The Correct Option is B

Step 1: Identify type of reactions.
Both reactions are redox reactions involving permanganate ion.

Step 2: Balance reaction (i) in acidic medium.
\[ MnO_4^- + SO_3^{2-} \rightarrow Mn^{2+} + SO_4^{2-} \]
Balancing gives:
\[ 2MnO_4^- + 5SO_3^{2-} + 6H^+ \rightarrow 2Mn^{2+} + 5SO_4^{2-} + 3H_2O \]
So:
\[ (a)=5,\quad (b)=6,\quad (c)=3 \]

Step 3: Balance reaction (ii) in basic medium.
\[ S_2O_3^{2-} + MnO_4^- \rightarrow MnO_2 + SO_4^{2-} \]
Balancing gives:
\[ 3S_2O_3^{2-} + 8MnO_4^- + H_2O \rightarrow 8MnO_2 + 6SO_4^{2-} + OH^- \]
So:
\[ (d)=8 \]

Step 4: Collect all coefficients.
\[ (a)=5,\quad (b)=6,\quad (c)=3,\quad (d)=8 \]

Step 5: Match with options.
Correct option is (B).

Step 6: Interpretation.
Permanganate acts as oxidizing agent in both reactions.

Step 7: Final conclusion.
\[ \boxed{(a)=5,\,(b)=6,\,(c)=3,\,(d)=8} \]