Question 5
What is limestone (CaCO3) fed into the blast furnace for?
The right answer is the one marked above.
To remove the impurities in the ore as slag. The CaO from the decomposition of the limestone reacts with the silica and alumina and forms slag.
It is CO that does the reducing, and coke that produces the CO. Decomposing limestone absorbs heat — it does not heat the furnace.