Science (086) — AI-generated practice question

| | Roasting | Calcination |
|---|---|---|
| Definition | Heating sulphide or carbonate ores in excess of air below their melting point | Heating carbonate or hydroxide ores in limited/absence of air below their melting point |
| Product | Oxide of the metal + SO₂ gas | Oxide of the metal + CO₂ / water vapour |

Example of Roasting (sulphide ore of zinc):

$$2\text{ZnS} + 3\text{O}_2 \xrightarrow{\Delta} 2\text{ZnO} + 2\text{SO}_2$$

Example of Calcination (carbonate ore of zinc):

$$\text{ZnCO}_3 \xrightarrow{\Delta} \text{ZnO} + \text{CO}_2$$

Source: Metals and Non-metals, Extraction of Metals

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• Examiners expect one clear distinguishing point + one example each with a balanced equation — that earns all 3 marks.
• The key distinction is excess air (roasting) vs limited/no air (calcination), and sulphide ore vs carbonate/hydroxide ore.
• ZnS/ZnO and ZnCO₃/ZnO are the standard NCERT examples; you may also use Cu₂S or CaCO₃.
• Do not confuse calcination with decomposition in general — it is specifically applied to ores in metallurgy.