A pale green solid dissolves in water to give a pale green solution that gives a deep blue precipitate with K3[Fe(CN)6]. The cation present, and the moles of KMnO4 needed in acid to oxidise 1 mol of it (MnO4- + 5Fe^2+ + 8H+ -> Mn^2+ + 5Fe^3+ + 4H2O), are

JEE Advanced levelSingle correct optionDifficulty 3 of 3qc195

A pale green solid dissolves in water to give a pale green solution that gives a deep blue precipitate with $K X_{3} [Fe (CN) X_{6}]$ . The cation present, and the moles of $KMnO X_{4}$ needed in acid to oxidise 1 mol of it ( $MnO X_{4} X^{-} + 5 Fe X^{2 +} + 8 H X^{+} Mn X^{2 +} + 5 Fe X^{3 +} + 4 H X_{2} O$ ), are

A pale green solution and Turnbull's blue with hexacyanoferrate(III) identify

Fe X^{2 +}

. By the equation 5 mol

Fe X^{2 +}

react with 1 mol

MnO X_{4} X^{-}

(5 electrons), so 1 mol needs

1/5 = 0.2

mol. 0.6 would come from the neutral-medium stoichiometry.