\(KMnO_4\) is a strong oxidizing agent in acidic medium. To provide acidic medium \(H_2SO_4\) is used instead of \(HCl\). This is because
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → HCl is oxidized by KMnO4 to Cl2
Acidified permanganate (E° \( \ce{MnO4^{-}} \)/\( \ce{Mn^{2+}} \) = +1.51 V) is a stronger oxidising agent than chlorine (E° \( \ce{Cl2} \)/\( \ce{Cl^{-}} \) = +1.36 V), so it oxidises the chloride ions of hydrochloric acid:
\( \ce{2MnO4^{-}} \) + \( \ce{16H^{+}} \) + \( \ce{10Cl^{-}} \) → \( \ce{2Mn^{2+}} \) + \( \ce{5Cl2} \) + \( \ce{8H2O} \)
Part of the \( \ce{KMnO4} \) is then used up by the acid instead of the substance being titrated, and the result is wrong. Sulphuric acid is not oxidised by \( \ce{KMnO4} \), so it is used to make the medium acidic.
Why the other options are incorrect
Option (1) H2SO4 is a stronger acid than HCl — Incorrect. HCl is in fact the stronger acid; acid strength is not the reason.
Option (3) H2SO4 is a dibasic acid — Incorrect. Dibasic means each molecule gives two \( \ce{H+} \); that changes only how much acid is needed, not whether the acid reacts with \( \ce{MnO4-} \).
Option (4) Rate is faster in the presence of H2SO4 — Incorrect. HCl would not slow the reaction down; it would use up \( \ce{KMnO4} \) by being oxidised to \( \ce{Cl2} \).
NCERT (2026-27 edition):
Potassium Permanganate – …
