In given reaction \(3MnO_4^{2-} + 4H^+ \longrightarrow 2MnO_4^- + MnO_2 + 2H_2O\) oxidation state shown by \(Mn\) are
(A) VI
(B) II
(C) VII
(D) IV
(E) V
Choose the correct answers from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A, C and D only
The reaction is a disproportionation: manganese(VI) in the manganate ion is unstable in acidic solution and is oxidised and reduced at the same time, to manganese(VII) and manganese(IV). The oxidation state of Mn in each species, with O = −2:
\( \ce{MnO4^2-}: \ x + 4(-2) = -2 \Rightarrow x = +6 \)
\( \ce{MnO4^-}: \ x + 4(-2) = -1 \Rightarrow x = +7 \)
\( \ce{MnO2}: \ x + 2(-2) = 0 \Rightarrow x = +4 \)
\( \ce{3MnO4^2- + 4H^+ -> 2MnO4^- + MnO2 + 2H2O} \)
(A) VI — Correct. Mn is +6 in the green manganate ion.
(B) II — Incorrect. No \( \ce{Mn^{2+}} \) appears; +2 is reached when permanganate is reduced in acidic solution.
(C) VII — Correct. Mn is +7 in the purple permanganate ion.
(D) IV — Correct. Mn is +4 in \( \ce{MnO2} \).
(E) V — Incorrect. No Mn(V) species takes part in this reaction.
NCERT (2026-27 edition):
Potassium Permanganate – “Potassium permanganate is prepared by fusion of MnO2 with an alkali metal hydroxide and an oxidising agent like KNO3. This produces the dark green K2MnO4 which disproportionates in a neutral or acidic solution to give permanganate.”
\( \ce{3MnO4^2- + 4H+ -> 2MnO4^- + MnO2 + 2H2O} \)