Which one is not a conductor of electricity?

$NaOH$ is manufactured by the electrolysis of a brine solution. The products of the reaction are:

Which gas is produced at the cathode when $NaOH$ is prepared by the chlor-alkali process?

The platinum electrodes were immersed in a solution of cupric sulphate and electric current was passed through the solution. After some time,it was found that the colour of copper sulphate disappeared with the evolution of gas at the electrode. The colourless solution contains:

Which of the following substances conducts electricity?

Electrolysis of aqueous $Na_2SO_4$ was carried out by passing a current of $3 \ A$ for $10 \ min$. The volume of the gas $(L)$ at $STP$ at the anode of the cell is approximately