Which of the following pairs of transition metal ions is the strongest oxidizing agent?

\(Mn^{3+}\) and \(Fe^{3+}\)

The correct answer is option 4. \(Mn^{3+}\) and \(Fe^{3+}\).

To determine which pair of transition metal ions is the strongest oxidizing agent, we need to compare their standard reduction potentials. The standard reduction potential (\(E^\circ\)) of an ion indicates its tendency to gain electrons and be reduced. A higher reduction potential means that the ion is a stronger oxidizing agent, as it can more easily accept electrons.

Here are the standard reduction potentials for the relevant redox couples:

\(Fe^{2+} / Fe^{3+}\): \(Fe^{3+} + 3e^- \rightarrow Fe\): \(E^\circ = +0.77 \text{ V}\)

\(Mn^{2+} / Mn^{3+}\): \(Mn^{3+} + 3e^- \rightarrow Mn^{2+}\): \(E^\circ = +1.57 \text{ V}\)

\(Cu^{2+} / Cu^{+}\): \(Cu^{2+} + 2e^- \rightarrow Cu^{+}\): \(E^\circ = +0.15 \text{ V}\)

\(Ti^{2+} / Ti^{3+}\): \(Ti^{3+} + 3e^- \rightarrow Ti^{2+}\): \(E^\circ = +0.08 \text{ V}\)

\(Ni^{2+} / Ni\): \(Ni^{2+} + 2e^- \rightarrow Ni\): \(E^\circ = -0.23 \text{ V}\)

\(Cr^{3+} / Cr^{2+}\): \(Cr^{3+} + 3e^- \rightarrow Cr^{2+}\): \(E^\circ = +1.33 \text{ V}\)

\(Mn^{3+} / Mn^{2+}\): As mentioned above, \(Mn^{3+} / Mn^{2+}\) has \(E^\circ = +1.57 \text{ V}\).

\(Fe^{3+} / Fe^{2+}\): \(Fe^{3+} + e^- \rightarrow Fe^{2+}\): \(E^\circ = +0.77 \text{ V}\)

Analysis

\(Mn^{3+}\) has the highest reduction potential among the ions listed. Thus, it is the strongest oxidizing agent. \(Fe^{3+}\) also has a relatively high reduction potential but is lower than that of \(Mn^{3+}\)

Therefore, the pair \(Mn^{3+}\) and \(Fe^{3+}\) is the strongest oxidizing agent since \(Mn^{3+}\) is the strongest oxidizing ion among the ones listed.