Question:

Given
\(\mathrm{Fe^{3+}(aq)} + e^- \rightarrow \mathrm{Fe^{2+}(aq)};\ E^0 = +0.77\ \mathrm{V}\)
\(\mathrm{Al^{3+}(aq)} + 3e^- \rightarrow \mathrm{Al(s)};\ E^0 = -1.66\ \mathrm{V}\)
\(\mathrm{Br_2(aq)} + 2e^- \rightarrow 2\mathrm{Br^-};\ E^0 = +1.09\ \mathrm{V}\)
Considering the electrode potentials, which of the following represents the correct order of reducing power?

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The lower (more negative) the reduction potential of a couple, the stronger the reducing power of its reduced form.
Updated On: Nov 11, 2026
  • \(\mathrm{Fe^{2+}} \lt \mathrm{Al} \lt \mathrm{Br^-}\)
  • \(\mathrm{Br^-} \lt \mathrm{Fe^{2+}} \lt \mathrm{Al}\)
  • \(\mathrm{Al} \lt \mathrm{Br^-} \lt \mathrm{Fe^{2+}}\)
  • \(\mathrm{Al} \lt \mathrm{Fe^{2+}} \lt \mathrm{Br^-}\)
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The Correct Option is B

Solution and Explanation

Reducing power of the reduced form increases as the standard reduction potential of its couple decreases.
\(E^0\): \(\mathrm{Br_2/Br^-} = +1.09\) V, \(\mathrm{Fe^{3+}/Fe^{2+}} = +0.77\) V, \(\mathrm{Al^{3+}/Al} = -1.66\) V.
Order of \(E^0\): \(\mathrm{Al^{3+}/Al} \lt \mathrm{Fe^{3+}/Fe^{2+}} \lt \mathrm{Br_2/Br^-}\), so the reducing power order is \(\mathrm{Br^-} \lt \mathrm{Fe^{2+}} \lt \mathrm{Al}\).
Answer: (2) \(\mathrm{Br^-} \lt \mathrm{Fe^{2+}} \lt \mathrm{Al}\)
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