Which one of the following reactions does not occur during extraction of copper?

Four reactions are listed. We need to identify which one does NOT occur during the extraction of copper from copper pyrites (CuFeS$$_2$$). Copper is extracted through the following steps:

Roasting: The ore is heated in air to convert iron sulfide to iron oxide: $$2\text{FeS} + 3\text{O}_2 \to 2\text{FeO} + 2\text{SO}_2$$ This is Option B — it occurs during copper extraction.

Slag formation: SiO$$_2$$ is added as a flux and reacts with FeO to form slag: $$\text{FeO} + \text{SiO}_2 \to \text{FeSiO}_3$$ This is Option D — it occurs during copper extraction.

Partial roasting of Cu$$_2$$S: $$2\text{Cu}_2\text{S} + 3\text{O}_2 \to 2\text{Cu}_2\text{O} + 2\text{SO}_2$$ This is Option A — it occurs during copper extraction.

Option C states: CaO + SiO$$_2$$ $$\to$$ CaSiO$$_3$$. In copper extraction, the flux used is SiO$$_2$$, which reacts with FeO (not CaO). CaO is not involved in copper extraction. The reaction CaO + SiO$$_2$$ $$\to$$ CaSiO$$_3$$ occurs in iron extraction (blast furnace), not copper extraction.

Answer: Option C