Question

Given $E _{ Cl _{2} / Cl ^{-}}^{\circ}=1 . 36\, V,\, E _{ Cr ^{3+} / Cr }^{\circ}=-7 \cdot 74\, V$ $E _{ Cr _{2} O _{7}^{2-} / Cr ^{3+}}^{\circ}=1 .33\, V,\, E _{ MnO _{4}^{-} / Mn ^{2}+}^{\circ}=1. 51\, V$ Among the following, the strongest reducing agent is:

• A. $Cr^{3+}$
• B. $Cl^{-}$
• C. $Cr$
• D. $Mn^{2+}$

Answer 1

Answer: (C)

$Cr$

Answer 2

For $Cr ^{3+}, \,E _{ Cr ^{3+} / Cr _{2} O _{7}^{2-}}=-1.33\, V$

For $Cl ^{-}, \, E _{ Cl ^{-} / Cl _{2}}^{\circ}=-1.36\, V$

For $Cr , \, E _{ Cr / Cr ^{3+}}^{\circ}=0.74\, V$

For $Mn ^{2+}, E _{ Mn ^{2+} / MnO _{4}^{-}}^{\circ}=-1.51\, V$

Positive $E^{\circ}$ is for $Cr$, hence it is strongest reducing agent.