Electrolysis of brine solution
$NaCl ( aq .) \longrightarrow Na _{( aq )}^{+}+ Cl _{\text {(aq) }}^{+}$
At anode $: 2 Cl _{\text {(aq.) }}^{+} \longrightarrow \underset{\text { (Major) }}{ Cl _2( g )+2 e ^{-}}$
$2 H _2 O _{(\ell)} \longrightarrow \underset{\text { Minor }}{ O _{2( g )}}+4 H _{( aq )}^{+}+4 e ^{-}$
At Cathode : $2 H _2 O _{(\ell)}+2 e ^{-} \longrightarrow H _{2( g )} \uparrow+2 OH _{( aq )}^{-}$
$2 Na ^{+}+2 OH ^{-} \longrightarrow 2 NaOH$