CBSE Class 10 Science 2020 · Paper 31/1/1 · Question 25

Carbon cannot reduce the oxides of sodium, magnesium and aluminium because these metals have more affinity for oxygen than carbon has, so carbon cannot take the oxygen away from their oxides. These metals are placed towards the top of the reactivity series, with potassium and calcium, above zinc and iron. They are obtained by electrolytic reduction of their molten compounds (molten chlorides, or the molten oxide for aluminium): electricity is passed through the molten compound and the metal is deposited at the cathode. Example: sodium is extracted by the electrolysis of molten sodium chloride. Molten $\text{NaCl}$ is taken in an electrolytic cell; on passing electricity, sodium is deposited at the cathode and chlorine is liberated at the anode. At the cathode: ${\text{Na}}^{+}+e^{-}⟶\text{Na}$ At the anode: $2{\text{Cl}}^{-}⟶{\text{Cl}}_2+2e^{-}$ Overall: $2\text{NaCl}(l)⟶2\text{Na}(l)+{\text{Cl}}_2(g)$ Any other correct example, such as magnesium from molten magnesium chloride, earns the same credit.