For the reduction of $\mathrm{NO}_3^{-}$ion in an aqueous solution $E^{\circ}$ is $+0.96 \mathrm{~V}$.…
For the reduction of $\mathrm{NO}_3^{-}$ion in an aqueous solution $E^{\circ}$ is $+0.96 \mathrm{~V}$. Values of $E^{\circ}$ for some metal ions are given below.
$$
\begin{aligned}
& \mathrm{V}^{2+}(a q)+2 e^{-} \longrightarrow \mathrm{V} ; E^{\circ}=-1.19 \mathrm{~V} \\
& \mathrm{Fe}^{3+}(a q)+3 e^{-} \longrightarrow \mathrm{Fe} ; \mathrm{E}^{\circ}=-0.04 \mathrm{~V} \\
& \mathrm{Au}^{3+}(a q)+3 e^{-} \longrightarrow \mathrm{Au} ; E^{\circ}=+1.40 \mathrm{~V}
\end{aligned}
$$
$$
\mathrm{Hg}^{2+}(a q)+2 e^{-} \longrightarrow \mathrm{Hg} ; E^{\circ}=+0.86 \mathrm{~V}
$$
The pair(s) of metals that is (are) oxidised by $\mathrm{NO}_3^{-}$in aqueous solution is (are)
$\mathrm{V}$ and $\mathrm{Hg}$
$\mathrm{Hg}$ and $\mathrm{Fe}$
Fe and Au
$\mathrm{Fe}$ and $\mathrm{V}$
Solution
The species having less reduction potential with respect to $\mathrm{NO}_3^{-}\left(E^{\circ}=0.96 \mathrm{~V}\right)$ will be oxidised by $\mathrm{NO}_3^{-}$; These species are $\mathrm{V}, \mathrm{Fe}, \mathrm{Hg}$.