The reaction 2I^- + S2O8^2- -> I2 + 2SO4^2- is catalysed by Fe^3+. Given E deg(Fe^3+/Fe^2+) = +0.77 V, E deg(I2/I^-) = +0.54 V and E deg(S2O8^2-/SO4^2-) = +2.01 V, which pair of steps is a feasible mechanism?

2Fe^3+ + 2I^- -> 2Fe^2+ + I2 followed by 2Fe^2+ + S2O8^2- -> 2Fe^3+ + 2SO4^2-

2Fe^3+ + S2O8^2- -> 2Fe^2+ + 2SO4^2- followed by 2Fe^2+ + 2I^- -> 2Fe^3+ + I2

2Fe^2+ + I2 -> 2Fe^3+ + 2I^- followed by 2Fe^3+ + S2O8^2- -> 2Fe^2+ + 2SO4^2-

Fe^3+ + 2I^- -> Fe^2+ + I2 followed by Fe^2+ + S2O8^2- -> Fe^3+ + SO4^2-

JEE Advanced levelSingle correct optionDifficulty 3 of 3df045

The reaction $2 I X^{-} + S X_{2} O X_{8} X^{2 -} I X_{2} + 2 SO X_{4} X^{2 -}$ is catalysed by $Fe X^{3 +}$ . Given $E^{\circ} (Fe X^{3 +} / Fe X^{2 +}) = + 0.77 V$ , $E^{\circ} (I X_{2} / I X^{-}) = + 0.54 V$ and $E^{\circ} (S X_{2} O X_{8} X^{2 -} / SO X_{4} X^{2 -}) = + 2.01 V$ , which pair of steps is a feasible mechanism?

A $2 Fe X^{3 +} + 2 I X^{-} 2 Fe X^{2 +} + I X_{2}$ followed by $2 Fe X^{2 +} + S X_{2} O X_{8} X^{2 -} 2 Fe X^{3 +} + 2 SO X_{4} X^{2 -}$
B $2 Fe X^{3 +} + S X_{2} O X_{8} X^{2 -} 2 Fe X^{2 +} + 2 SO X_{4} X^{2 -}$ followed by $2 Fe X^{2 +} + 2 I X^{-} 2 Fe X^{3 +} + I X_{2}$
C $2 Fe X^{2 +} + I X_{2} 2 Fe X^{3 +} + 2 I X^{-}$ followed by $2 Fe X^{3 +} + S X_{2} O X_{8} X^{2 -} 2 Fe X^{2 +} + 2 SO X_{4} X^{2 -}$
D $Fe X^{3 +} + 2 I X^{-} Fe X^{2 +} + I X_{2}$ followed by $Fe X^{2 +} + S X_{2} O X_{8} X^{2 -} Fe X^{3 +} + SO X_{4} X^{2 -}$

A step is feasible when the oxidant's

E^{\circ}

exceeds the reductant couple's.

Fe X^{3 +}

(+0.77) can oxidise

I X^{-}

(+0.54), and

S X_{2} O X_{8} X^{2 -}

(+2.01) can oxidise

Fe X^{2 +}

. The two steps sum to the overall reaction with

Fe X^{3 +}

regenerated, and both are balanced. The other options reverse feasible steps or are unbalanced.