Paragraph: Redox reaction play a pivotal role in chemistry and...

Paragraph: Redox reaction play a pivotal role in chemistry and biology. The values of standard redox potential $\left(E^{{}^{\circ}}\right)$ of two half-cell reactions decide which way the reaction is expected to proceed. A simple example is a Daniel cell in which zinc goes into solution and copper gets deposited. Given below are a set of half-cell reactions (acidic medium) along with their $E^{{}^{\circ}}(V$ with respect to normal hydrogen electrode) values. Using this data obtain the correct explanations to Questions 14-19. $$\begin{array}{cl}\mathrm{I}_{2}+2 e^{-} \longrightarrow 2 \mathrm{I}^{-}& E^{{}^{\circ}}=0.54 \\ \mathrm{Cl}_{2}+2 e^{-} \longrightarrow 2 \mathrm{Cl}^{-}& E^{{}^{\circ}}=1.36 \\ \mathrm{Mn}^{3+}+e^{-} \longrightarrow \mathrm{Mn}^{2+}& E^{{}^{\circ}}=1.50 \\ \mathrm{Fe}^{3+}+e^{-} \longrightarrow \mathrm{Fe}^{2+}& E^{{}^{\circ}}=0.77 \\ \mathrm{O}_{2}+4 \mathrm{H}^{+}+4 e^{-} \longrightarrow 2 \mathrm{H}_{2}\mathrm{O}& E^{{}^{\circ}}=1.23 \end{array}$$ Question: While $\mathrm{Fe}^{3+}$ is stable, $\mathrm{Mn}^{3+} is not stable$ in acid solution because