Removal of acidic impurities via slag formation in blast furnace

Steps:

• Identify acidic impurity in iron ore as SiO₂ from silica.
• Recognize CaO as basic flux added to neutralize acidic SiO₂.
• Note reaction forms molten slag CaSiO₃, which separates and is removed.
• Eliminate other options as they involve fuel combustion or iron reduction, not impurity removal.

Why D is correct:

• CaO (basic oxide) reacts with SiO₂ (acidic oxide) to form slag CaSiO₃ per acid-base neutralization in metallurgy, removing silica impurity.

Why the others are wrong:

• A: Combustion of coke to produce CO₂ gas for reduction process.
• B: Oxidation of iron by CO to form FeO, an intermediate step in iron production.
• C: Reduction of iron oxide Fe₂O₃ to metallic iron using CO.

Final answer: D