In the extraction of copper, its sulphide ore is heated in a reverberatory furnace after mixing with silica to:

In the extraction of copper from its sulphide ore, the ore is heated in a reverberatory furnace after mixing with silica.

Purpose of adding silica (SiO$$_2$$):

During the smelting process, the ore contains iron sulphide (FeS) as an impurity. The FeS gets oxidized to FeO. Silica acts as a flux and combines with the basic impurity FeO to form iron silicate (slag):

$$\text{FeO} + \text{SiO}_2 \to \text{FeSiO}_3 \text{ (slag)}$$

This slag is immiscible with the matte (Cu$$_2$$S) and floats on top, allowing easy separation. This removes iron impurities from the copper matte.

The correct answer is Option 4: Remove FeO as FeSiO$$_3$$.