For a given half cell, \(\mathrm{Al}^{3+}+3 \mathrm{e}^{-} \rightarrow \mathrm{Al}\) on increasing of aluminium ion, the electrode potential will

\(\mathrm{Al}^{3+}+3 \mathrm{e}^{-} \rightarrow \mathrm{Al}(\mathrm{s})\)
\(\begin{aligned}
& \mathrm{E}_{\text {Red }}=\mathrm{E}_{\text {Red }}^{\mathrm{o}}-\frac{0.0591}{3} \log \frac{[\mathrm{Al}(\mathrm{~s})]}{\left[\mathrm{Al}^{3+}\right]} \\
& \mathrm{E}_{\text {Red }}=\mathrm{E}_{\text {Red }}^{\mathrm{o}}-\frac{0.0591}{4} \log \frac{1}{\left[\mathrm{Al}^{3+}\right]}[\text { Since active mass of solid }=1] \\
& \mathrm{E}_{\text {Red }}=\mathrm{E}_{\text {Red }}^{\mathrm{o}}+\frac{0.0591}{3} \log \left[\mathrm{Al}^{3+}\right]
\end{aligned}\)

So \(E_{\text {Red }} \propto\left[\mathrm{Al}^{3+}\right] \propto \operatorname{conc}^{\mathrm{n}}\) of \(\mathrm{Al}^{3+}\)