How is limestone used in iron extraction
A. Oxidation of Fe ore
B. Reduction of Fe ore
C. Formation of slag
D. Purification of Fe formed

Hint: Iron is extracted from hematite by smelting. In the smelting of iron limestone is decomposed to calcium oxide and carbon dioxide. This calcium oxide combines with silicon dioxide present in the blast furnace.

Complete Step by Step Answer:
Limestone is actually calcium carbonate. Calcium carbonate in a blast furnace decomposes to produce calcium dioxide along with carbon dioxide. The reaction can be given as follows:
$CaC{{O}_{3}}\to CaO+C{{O}_{2}}$
In this reaction one mole of calcium carbonate is heated to form one mole of metal oxide ore that is calcium oxide along with carbon dioxide gas.

Blast furnace contains silicon dioxide. This calcium dioxide combines with the silicon dioxide to form calcium silicate. The reaction can be given as follows:
$CaO+Si{{O}_{2}}\to CaSi{{O}_{3}}$

Slag is a compound of calcium oxide and silicon dioxide. Thus slag is produced in the metallurgy of iron, when limestone is added to the blast furnace.
Thus the correct option is C.

Note: Due to the action of limestone metal is smelted out of its ore and the ore appears to be in a glassy state. This glassy appearance of the ore is caused by the formation of slag during the smelting process on the surface of the ore.