For $I_{2} + 2 e \to 2 I^{-}$ , standard reduction potential = + 0.54 volt. For $2 {Br}^{-} \to {Br}_{2} + 2 e^{-}$ , standard oxidation potential = – 1.09 volt. For $Fe \to {Fe}^{2 +} + 2 e^{-}$ standard oxidation potential = + 0.44 volt. Which of the following reactions is non-spontaneous?

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$Fe + {Br}_{2} \to {Fe}^{2 +} + 2 {Br}^{-}$

$I_{2} + 2 {Br}^{-} \to 2 I^{-} + {Br}_{2}$

$Fe + I_{2} \to {Fe}^{2 +} + 2 I^{-}$

${Br}_{2} + 2 I^{-} \to 2 {Br}^{-} + I_{2}$

answer is D.

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Detailed Solution

A redox reaction in which SRP of oxidising agent is lesser than SRP of reducing agent is non-spontaneous and does not occurs.

Alternatively, If E_cell comes to be negative the reaction is non-spontaneous and does not occur.

For option (4), E⁰= E⁰(Cathode)-E⁰(anode)= +0.54V-1.09V=-0.55V ;

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