The correct option(s) related to the extraction of iron from its ore in the blast furnace operating in the…

(A) Limestone is added to remove silica as impurity.

$\mathrm{CaO} + {\mathrm{SiO}}_2 \to {\mathrm{CaSiO}}_3 (\mathrm{in} \mathrm{the} \mathrm{temperature} \mathrm{range} 900 – 1500 \mathrm{K})$

(B) Pig iron obtained from blast furnace contains $4\%$ carbon and many other impurities (eg. $\mathrm{S},\mathrm{P},\mathrm{Si},\mathrm{Mn}$) in small amount.

 In fusion zone molten iron becomes heavy by absorbing elemental impurities and produces Pig iron. (in the temperature range 900 – 1500 K)

(C) Coke $\left(\mathrm{C}\right)$ converts ${\mathrm{CO}}_2$ in $\mathrm{CO}$.

$\mathrm{C}+{\mathrm{CO}}_2\to 2\mathrm{CO}$

(D) Exhaust gases consist of $\mathrm{CO}$ and ${\mathrm{CO}}_2$.

Exhaust gases does not contain NO₂

Hence, (A,B,C) are correct.