If same quantity of electricity is passed through three electrolytic cells containing ${\text{FeSO}}_{\text{4}}{\text{,\hspace{0.17em}Fe}}_{\text{2}}{\left({\text{SO}}_{\text{4}}\right)}_{\text{3}}\text{,\hspace{0.17em}Fe}{\left({\text{NO}}_{\text{3}}\right)}_{\text{3}}$ in series then

${\text{FeSO}}_{\text{4}}{\text{,\hspace{0.17em}Fe}}^{\text{+2}}\text{\hspace{0.17em}+\hspace{0.17em}\hspace{0.17em}}\to \text{\hspace{0.17em}Fe\hspace{0.17em}\hspace{0.17em}}$        $\text{IF\hspace{0.17em}=\hspace{0.17em}}\frac{\text{1}}{\text{2}}\text{\hspace{0.17em}mol Fe}$

$\text{Fe}{\left({\text{NO}}_3\right)}_{\text{3}},{\text{\hspace{0.17em}Fe}}^{\text{+3}}\to \text{\hspace{0.17em}Fe}$        $\text{IF\hspace{0.17em}=\hspace{0.17em}}\frac{\text{1}}{\text{3}}\text{\hspace{0.17em}mol\hspace{0.17em}Fe}$

${\text{Fe}}_{\text{2}}{\left({\text{SO}}_{\text{4}}\right)}_{\text{3}}{\text{Fe}}^{+3}\to \text{Fe}$          $\text{IF\hspace{0.17em}=\hspace{0.17em}}\frac{\text{1}}{\text{3}}\text{\hspace{0.17em}mol\hspace{0.17em} Fe}$

$\Rightarrow$Amount of $\text{Fe}$ deposited in $\text{Fe}{\left({\text{NO}}_{\text{3}}\right)}_{\text{3}}=$Amount of $\text{Fe}$deposited in ${\text{Fe}}_{\text{2}}{\left({\text{SO}}_{\text{4}}\right)}_{\text{3}}$

$\Rightarrow$Amount of $\text{Fe}$deposited in ${\text{Fe}}_{\text{2}}{\left({\text{SO}}_{\text{4}}\right)}_{\text{3}}\text{\hspace{0.17em}=\hspace{0.17em}}\frac{\text{1}}{\text{2}}\text{\hspace{0.17em}:\hspace{0.17em}}\frac{\text{1}}{\text{3}}$

$\Rightarrow$At Anode: ${\text{4\hspace{0.17em}OH}}^{\text{-}}\to {\text{\hspace{0.17em}O}}_{\text{2}}{\text{\hspace{0.17em}+\hspace{0.17em}2H}}_{\text{2}}\text{O\hspace{0.17em}}$in all cases same amount of gas is evolved