Which of the following electrolytes can be used to obtain $H_2S_2O_8$ by the process of electrolysis?

Predict the products of electrolysis in each of the following:
$(i)$ An aqueous solution of $AgNO_3$ with silver electrodes.
$(ii)$ An aqueous solution of $AgNO_3$ with platinum electrodes.
$(iii)$ $A$ dilute solution of $H_2SO_4$ with platinum electrodes.
$(iv)$ An aqueous solution of $CuCl_2$ with platinum electrodes.

During the electrolysis of $NaCl$ solution,$H_2$ gas is liberated at the cathode when a $Pt$ electrode is used,whereas sodium amalgam is formed when a $Hg$ cathode is used. What is the reason for this?

When sodium chloride solution is electrolysed,the gas that is liberated at the cathode is

The cell used for the electrolysis of fused $NaCl$ is

Electrolytes can conduct electricity because