# A solution containing one mole per litre each of $Cu(NO_3)_2,AgNO_3,Hg_2(NO_3)_2$ is being electrolysed by using inert electrodes.The values of standard potentials are $E^{\large\circ}_{Ag^+|Ag}=0.80V,E^{\large\circ}_{Hg_2^{2+}|Hg}=0.79V,E^{\large\circ}_{Cu^{2+}|Cu}=0.34V,E^{\large\circ}_{Mg^{2+}|Mg}=-2.3V$ with increasing voltage,the sequence of deposition of metals on the cathode will be

$\begin{array}{1 1}Ag,Hg,Cu,Mg\\Mg,Cu,Hg,Ag\\Ag,Hg,Cu\\Cu,Hg,Ag\end{array}$

Electrolysis will occur if $E_{ext} > E_{galvanic}$.The value of $E_{galvanic}$ (in which metal is oxidized) is $E_{H_2O|O_2|Pt}-E_M^{n+}|M$.Hence,$E_{ext}$ will be reached in the order Ag,Hg and Cu.Hence,the sequence of deposition of metals on the cathode will be Ag,Hg and Cu.Before Mg is deposited,$H_2$ gas will be obtained by the reduction of $H_2O$