Why is that iron doe

Iron is quite reactive and so it does not occur as a metal in the crust of the earth. The common compounds formed are its oxide, a carbonate and a sulphide. The oxide ore of iron called haematite is more often used for extracting iron. The carbon and limestone which is mixed with iron ore is called the charge. This charge is responsible for the formation of iron metal. Coke acts the reducing agent and addition of limestone helps to remove the earthy impurities like sand from the blast furnace by forming fusible slag. Reduction of Iron(III)oxide or haematite to Iron: carbon monoxide reduces iron(III)oxide to iron metal
Fe₂O₃(s) + 3CO(g) 2Fe +3Co₂ (g)i) In the blast furnace limestone decomposes to form calcium oxide and carbon dioxide.
CaCO₃ (s) CaO(s) +CO₂(g)ii) This calcium oxide reacts with sand for form molten calcium silicate called slag.
CaO(s) + SiO₂ CaSiO₃(l)
                                 slag.