Some standard electrode potentials are shown in the table below.
Half-equationEθ/VS2O82−(aq)+2e−⇌2SO42−(aq)+2.01MnO4−(aq)+8H+(aq)+5e−⇌Mn2+(aq)+4H2O(l)+1.51Cr3+(aq)+e−⇌Cr2+(aq)−0.41Zn2+(aq)+2e−⇌Zn(s)−0.76 \begin{array}{lc} \text{Half-equation} & E^\theta / \text{V} \\ \hline \text{S}_2\text{O}_8^{2-}(\text{aq}) + 2e^- \rightleftharpoons 2\text{SO}_4^{2-}(\text{aq}) & +2.01 \\ \text{MnO}_4^-(\text{aq}) + 8\text{H}^+(\text{aq}) + 5e^- \rightleftharpoons \text{Mn}^{2+}(\text{aq}) + 4\text{H}_2\text{O}(\text{l}) & +1.51 \\ \text{Cr}^{3+}(\text{aq}) + e^- \rightleftharpoons \text{Cr}^{2+}(\text{aq}) & -0.41 \\ \text{Zn}^{2+}(\text{aq}) + 2e^- \rightleftharpoons \text{Zn}(\text{s}) & -0.76 \\ \end{array} Half-equationS2O82−(aq)+2e−⇌2SO42−(aq)MnO4−(aq)+8H+(aq)+5e−⇌Mn2+(aq)+4H2O(l)Cr3+(aq)+e−⇌Cr2+(aq)Zn2+(aq)+2e−⇌Zn(s)Eθ/V+2.01+1.51−0.41−0.76Which of the following species is the strongest reducing agent under standard conditions?
Zn2+(aq)\text{Zn}^{2+}(\text{aq})Zn2+(aq)
Zn(s)\text{Zn}(\text{s})Zn(s)
SO42−(aq)\text{SO}_4^{2-}(\text{aq})SO42−(aq)
Cr2+(aq)\text{Cr}^{2+}(\text{aq})Cr2+(aq)
