Answer: carbon monoxide gas.
- A coke burning directly
- B carbon monoxide gas
- C calcium oxide flux
- D molten silica slag
Correct answer: B. carbon monoxide gas
Explanation: In the cooler upper region, CO reduces the ore: Fe₂O₃ + 3CO → 2Fe + 3CO₂. Direct reduction by coke dominates only in the hotter lower zone.
An Ellingham diagram plots ΔG° of oxide formation against temperature for different metals; whichever line is LOWER (more negative ΔG°) at a given temperature reduces the oxide of any metal whose line sits above it - the basis of carbon reduction (Fe, Zn) vs electrolytic reduction (Al, Mg, Na) decisions.
Concept context
The science of extracting metals from ores and refining them for use. Covers concentration methods, reduction techniques, refining processes, and the thermodynamic principles that govern metal extraction.