The main function of limestone in the blast furnance is to

Analyze the question: The question asks about the role of limestone (CaCO₃) in the blast furnace used to extract iron from its ore (haematite, Fe₂O₃).

Concept: Iron ore contains impurities, mainly silica (SiO₂, sand). If these are not removed, they would clog the furnace and contaminate the iron. Limestone is added as a flux, which helps convert these impurities into a molten waste called slag.

Step-by-step solution:

1. Limestone decomposes at high temperature: CaCO₃ → CaO + CO₂

2. The calcium oxide (a basic oxide) reacts with silica (an acidic oxide): CaO + SiO₂ → CaSiO₃ (calcium silicate, the slag)

3. The slag is molten and less dense than the molten iron, so it floats on top and can be tapped off separately.

Checking the options:

• A. Reducing agent: wrong. The reducing agents are carbon and carbon(II) oxide (CO).
• B. Catalyst: wrong. Limestone is consumed in the reaction, so it is not a catalyst.
• C. Remove impurities: correct. It forms slag with silica and other impurities.
• D. Supply carbon(IV) oxide: CO₂ is produced, but it is not the main purpose. The CO₂ is then reduced by coke to CO, which is the actual reducing agent, so this is not the main function.

Tip: Remember "Limestone = Flux = Slag." Whenever you see limestone in the blast furnace, think of removing impurities (silica) as slag. Coke supplies heat and CO for reduction.