Partial Roasting of chalcopyrite produces:

The correct answer is Option (1) → \(Cu_2S\) and \(FeO\)

Chalcopyrite is \( \ce{CuFeS2} \). In partial roasting the ore is heated in a limited supply of air. Iron has a greater affinity for oxygen than copper, and copper has a greater affinity for sulphur, so the iron sulphide is oxidised first and copper stays as its sulphide:

    \( \ce{2CuFeS2 + O2 -> Cu2S + 2FeS + SO2} \)

    \( \ce{2FeS + 3O2 -> 2FeO + 2SO2} \)

Adding the two equations:

    \( \ce{2CuFeS2 + 4O2 -> Cu2S + 2FeO + 3SO2} \)

So the products are Cu₂S and FeO. The FeO is then removed with silica as slag, and copper stays in the matte as Cu₂S:

    \( \ce{FeO + SiO2 -> FeSiO3} \)

Why the other options are incorrect

• Option (2) \(Cu_2O\) and \(FeO\) — Incorrect. Cu₂S is oxidised to Cu₂O only later, in the converter, after the iron has been removed. Any Cu₂O formed earlier is turned back into Cu₂S by FeS:

      \( \ce{Cu2O + FeS -> FeO + Cu2S} \)

• Option (3) \(CuS\) and \(Fe_2O_3\) — Incorrect. Copper in the roasted ore is copper(I) sulphide, Cu₂S, not CuS, and iron goes to FeO, which forms the FeSiO₃ slag.

• Option (4) \(Cu_2O\) and \(Fe_2O_3\) — Incorrect. Both metals as oxides would need both sulphides fully oxidised. In partial roasting the air supply is limited, so copper stays as Cu₂S.

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Extraction of Copper from Cuprous Oxide [Copper(I) Oxide] – …