The correct answer is D. All the above.
To melt one tonne of cast iron, 700 m3 of air, 20 kg of limestone, and one quintal of coke are required.
Air is required for the combustion of coke, which is the main fuel used in blast furnaces. Limestone is used to remove impurities from the iron ore, and coke is used to provide heat and reduce the iron ore to molten iron.
The following is a more detailed explanation of each option:
- Option A: 700 m3 air is required.
Air is required for the combustion of coke, which is the main fuel used in blast furnaces. The combustion of coke produces carbon monoxide, which is a reducing agent that reduces the iron ore to molten iron.
The amount of air required for combustion depends on the type of coke used and the efficiency of the blast furnace. In general, about 700 m3 of air is required to melt one tonne of cast iron.
- Option B: 20 kg limestone is required.
Limestone is used to remove impurities from the iron ore. The impurities in the iron ore are mostly silica and alumina. These impurities react with the limestone to form calcium silicate and calcium aluminate. These compounds are then removed from the molten iron as slag.
The amount of limestone required depends on the type of iron ore used and the efficiency of the blast furnace. In general, about 20 kg of limestone is required to melt one tonne of cast iron.
- Option C: One quintal coke is required.
Coke is used to provide heat and reduce the iron ore to molten iron. Coke is made from coal that has been heated to a high temperature in the absence of air. This process removes the volatile components from the coal, leaving behind a solid fuel that is high in carbon.
The amount of coke required depends on the type of iron ore used and the efficiency of the blast furnace. In general, about one quintal of coke is required to melt one tonne of cast iron.