Which one of the following reactions does not take place in blast fur…

The correct answer is Option (4) → FeO + SiO₂ → FeSiO₃

In the blast furnace, iron oxides are reduced by carbon monoxide. In the lower temperature range (500–800 K) the reactions are:

    \( \ce{3Fe2O3 + CO -> 2Fe3O4 + CO2} \)

    \( \ce{Fe3O4 + 4CO -> 3Fe + 4CO2} \)

    \( \ce{Fe2O3 + CO -> 2FeO + CO2} \)

In the higher temperature range (900–1500 K), FeO is reduced: \( \ce{FeO + CO -> Fe + CO2} \). The silica impurity is removed as slag by the limestone flux, which first decomposes to CaO:

    \( \ce{CaCO3 -> CaO + CO2} \)

    \( \ce{CaO + SiO2 -> CaSiO3} \)

FeO is the very substance being reduced to iron, so it is not slagged off with silica. The reaction FeO + SiO₂ → FeSiO₃ belongs to the extraction of copper, where iron oxide is the impurity to be removed as slag.

• Option (1) 3Fe₂O₃ + CO → 2Fe₃O₄ + CO₂ — Takes place in the blast furnace. Reduction of Fe₂O₃ at 500–800 K.

• Option (2) Fe₃O₄ + 4CO → 3Fe + 4CO₂ — Takes place in the blast furnace. Reduction of Fe₃O₄ at 500–800 K.

• Option (3) Fe₂O₃ + CO → 2FeO + CO₂ — Takes place in the blast furnace. Reduction of Fe₂O₃ to FeO at 500–800 K.

• Option (4) FeO + SiO₂ → FeSiO₃ — Does not take place in the blast furnace. It is the slag-forming step of the extraction of copper.

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.