Explain how industrial production of sodium hydroxide is carried out by the Castner-Kellner cell.

(N/A) Sodium hydroxide is prepared commercially by the electrolysis of brine ($NaCl$ solution) in the Castner-Kellner cell. $A$ mercury cathode and a carbon anode are used.
At the cathode,sodium ions are reduced to sodium metal,which dissolves in mercury to form sodium amalgam $(Na-Hg)$:
$Na^{+} + e^{-} \xrightarrow{Hg} Na-Hg$
At the anode,chloride ions are oxidized to chlorine gas:
$Cl^{-} \rightarrow \frac{1}{2} Cl_{2} + e^{-}$
The sodium amalgam is then treated with water to produce sodium hydroxide and hydrogen gas:
$2Na-Hg + 2H_{2}O \rightarrow 2NaOH + 2Hg + H_{2}$
Properties: Sodium hydroxide is a white,translucent solid with a melting point of $591 \ K$. It is highly soluble in water,forming a strong alkaline solution. Its crystals are deliquescent and react with atmospheric $CO_{2}$ to form $Na_{2}CO_{3}$.
Uses: $(i)$ Manufacture of soap,paper,and artificial silk,$(ii)$ Petroleum refining,$(iii)$ Purification of bauxite,$(iv)$ Mercerising cotton fabrics,$(v)$ Preparation of pure fats and oils,and $(vi)$ As a laboratory reagent.