The main function of limestone in the blast furnace during the extraction of iron is to

Step 1: Analyze the question We are asked about the main function of limestone (CaCO₃) in the blast furnace used to extract iron from its ore (haematite, Fe₂O₃).

Step 2: Explain the concept Iron ore contains impurities, mainly silica (SiO₂, sand). If these stay in the furnace, they would clog it and contaminate the iron. Limestone is added to remove them by forming slag.

Step 3: Step-by-step solution

1. Limestone decomposes in the heat of the furnace: CaCO₃ → CaO + CO₂

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

3. Slag is molten and less dense than molten iron, so it floats on top and is tapped off separately.

Step 4: Check each option

• A. Catalyst: Wrong. Limestone is used up in forming slag, so it does not act as a catalyst.
• B. Remove impurities: Correct. It converts silica and other impurities into slag.
• C. Reducing agent: Wrong. The reducing agents are carbon (coke) and carbon(II) oxide (CO).
• D. Supply carbon(IV) oxide: CO₂ is produced when limestone decomposes, but this is not its main purpose. The CO₂ is later reduced by coke to CO, but coke is already the main source of that.

Answer: B. Remove impurities

Tip: Remember the pairing: Coke = fuel and reducing agent, Limestone = slag former (removes impurities), Haematite = the ore. Whenever you see "limestone" and "blast furnace," think slag.