Impurity Removal via Slag Formation

Steps:

• Identify the blast furnace process: Iron(III) oxide is reduced to iron, while SiO2 impurity must be removed without affecting iron production.
• Recall that acidic SiO2 reacts with basic CaO (from limestone) to form slag.
• Evaluate options: Check which reaction neutralizes SiO2 into a separable byproduct.
• Confirm C matches the standard acid-base reaction for slag.

Why C is correct:

• CaO (basic oxide) neutralizes acidic SiO2 to form CaSiO3 slag, which is molten and floats on molten iron for easy removal.

Why the others are wrong:

• A: Consumes Fe2O3 to form FeSiO3, reducing iron yield and incorporating iron into slag.
• B: Carbon reduces SiO2 to SiO gas, but this doesn't form separable slag and isn't the primary removal method.
• D: No reaction occurs between SiO2 and N2 in the furnace; nitrogen is inert here.

Final answer: C