How is sodium hydroxide prepared commercially from brine solution?

Explanation

Sodium hydroxide is prepared commercially by the electrolysis of brine solution in Castner Kellner cell using a mercury cathode and a carbon anode
(b) Sodium metal is discharged at the cathode and combines with mercury to form sodium amalgam.
c) Chlorine gas is evolved at the cathode
(d) The sodium amalgam thus obtained is treated with water to give sodium hydroxide.
At cathode: `Na^(+)` +e    to   Na (amalgam)
At anode: `CI^(-)      to    1//2CI_(2)uarr+e^(-)`
`2Na ("amalgam") + 2H_(2)O      to        underset("Sodium hydroxide")(2NaOH + 2Hg + H_(2)uarr)`