CBSE Class 10 Science 2019 · Paper 31/4/1 · Question 15

Metals in the middle of the reactivity series (zinc, iron, lead) are obtained by first converting their sulphide or carbonate ores into oxides, by roasting or calcination, and then reducing the oxides with a reducing agent such as carbon, for example $\text{ZnO}+\text{C}⟶\text{Zn}+\text{CO}$. Metals high up in the series (potassium, sodium, calcium, magnesium, aluminium) are obtained by the electrolysis of their molten chlorides or oxides, the metal being deposited at the cathode. The same process cannot be applied because these metals are very reactive: they have more affinity for oxygen than carbon has, so carbon cannot reduce their oxides. The method of extraction depends on the reactivity of the metal. The process used is electrolytic reduction; the metal obtained can then be purified by electrolytic refining.