The solution of nickel sulphate in which nickel rod is dipped is diluted 10 times. The potential of nickel

Reaction is:

${\mathrm{Ni}}^{2+}+2{\mathrm{e}}^{-}\to \mathrm{Ni}$

Nernst equation is:

$\mathrm{E}={\mathrm{E}}^{\circ }+\frac{0.059}{2}\log \left[{\mathrm{Ni}}^{2+}\right]$

After dilution:

${\mathrm{E}}_1={\mathrm{E}}_{\circ }-\frac{0.059}{2}\log \frac{\left[{\mathrm{Ni}}^{2+}\right]}{10}$

$$\begin{gathered} \mathrm{E}-{\mathrm{E}}_1=\frac{0.059}{2}\log \frac{\left[{\mathrm{Ni}}^{2+}\right]}{{\displaystyle \frac{\left[{\mathrm{Ni}}^{2+}\right]}{10}}} \\ {\mathrm{E}}_1=\mathrm{E}-30 \mathrm{mV} \end{gathered}$$

Therefore, the reduction potential of Ni decreases by 30 mV.