\( \ce{KMnO4 + H2SO4 + X -> MnSO4 + K2SO4 + H2O + CO2} \)
Identify X:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → C2H2O4
Acidified permanganate is a strong oxidising agent: in acid \( \ce{MnO4^{-}} \) is reduced to \( \ce{Mn^{2+}} \) (Mn: +7 → +2, 5 electrons). The products \( \ce{MnSO4} \), \( \ce{K2SO4} \), \( \ce{H2O} \) and CO2 show that X is oxidised to carbon dioxide at moderate temperature: X is oxalic acid, \( \ce{H2C2O4} \) (C: +3 → +4).
\( \displaystyle \text{Reduction:}\ \ \ce{MnO4^- + 8H^+ + 5e^- -> Mn^2+ + 4H2O}\quad(\times 2) \)
\( \displaystyle \text{Oxidation:}\ \ \ce{C2O4^2- -> 2CO2 + 2e^-}\quad(\times 5) \)
\( \displaystyle \ce{2KMnO4 + 3H2SO4 + 5H2C2O4 -> K2SO4 + 2MnSO4 + 8H2O + 10CO2} \)
The reaction is carried out at about 333 K and is used in the titration of oxalic acid with \( \ce{KMnO4} \).
Why the other options are incorrect
Option (1) C6H12O6 — Incorrect. Glucose is a reducing sugar, but it is not the carbon compound of this reaction. The reactions of acidified permanganate in the book list oxalate (oxalic acid) as the substance oxidised to carbon dioxide at 333 K, with 2 mol of \( \ce{MnO4^{-}} \) for 5 mol of oxalate.
Option (3) C2H6 — Incorrect. Ethane is a saturated hydrocarbon and is not oxidised by acidified \( \ce{KMnO4} \).
Option (4) C2H8 — Incorrect. There is no such compound; a two-carbon hydrocarbon can carry at most six hydrogen atoms (CnH2n+2).
NCERT (2026-27 edition):
Oxides and Oxoanions of Metals – “… Acidified permanganate solution oxidises oxalates to carbon dioxide, iron(II) to iron(III), nitrites to nitrates and iodides to free iodine. …
(c) Oxalate ion or oxalic acid is oxidised at 333 K:
\( \ce{5C2O4^2- + 2MnO4^- + 16H^+ -> 2Mn^2+ + 8H2O + 10CO2} \)”