Oxides of highly active metals like sodium, potassium and calcium are obtained by electrolytic reduction of fused metallic salts (halides and oxides) using inert electrodes.
Sodium
Electrolyte : Fused sodium chloride
Reaction : NaCl ⇌ Na+ + Cl-
Reaction at cathode : Na+ + e- ⟶ Na
Reaction at anode : Cl- - e- ⟶ Cl
Cl + Cl ⟶ Cl2
Potassium
Electrolyte : Fused potassium bromide
Reaction : KBr ⇌ K+ + Br-
Reaction at cathode : K+ + e- ⟶ K
Reaction at anode : Br- - e- ⟶ Br
Br + Br ⟶ Br2
Calcium
Electrolyte : Fused calcium chloride
Reaction : CaCl2 ⇌ Ca2+ + 2Cl-
Reaction at cathode : Ca2+ + 2e- ⟶ Ca
Reaction at anode : Cl- - e- ⟶ Cl
Cl + Cl ⟶ Cl2