During the smelting of copper pyrites in a reverberatory furnace, iron impurity is removed as:
Correct: C
Copper pyrites (CuFeS2) contain iron as an impurity. During smelting in a reverberatory furnace, the ore is roasted, converting some iron sulphide to iron oxide (FeO). Silica (SiO2) is then added as a flux, which reacts with the iron oxide to form fusible ferrous silicate (FeSiO3) slag. This slag, being lighter, floats on the molten copper matte and is easily skimmed off, thus removing the iron impurity.