The correct option(s) related to the extraction of iron from its ore in the blast furnace operating in the temperature range 900 - 1500 K is(are)

In a blast furnace the charge contains iron ore ($$Fe_2O_3$$ / $$Fe_3O_4$$), coke ($$C$$) and limestone ($$CaCO_3$$). The principal reactions that occur between $$900 - 1500 \text{ K}$$ are summarised below, followed by the assessment of each option.

Reaction of limestone and removal of silica
$$CaCO_3 \;\xrightarrow{\,T\,}\; CaO + CO_2$$
$$CaO + SiO_2 \;\rightarrow\; CaSiO_3$$ (fusible slag)
Thus limestone supplies $$CaO$$ which combines with the acidic impurity $$SiO_2$$ to give calcium silicate slag.

Reactions involving coke
(i) $$C + O_2 \;\rightarrow\; CO_2 + \text{heat}$$
(ii) $$C + CO_2 \;\rightarrow\; 2\,CO$$ (Boudouard reaction)
The carbon monoxide produced in (ii) rises up and reduces the iron oxides.

Composition of molten iron (pig iron)
The iron tapped at the bottom (pig iron) dissolves a considerable amount of carbon along with traces of $$Si, P, S$$ etc. The carbon content is roughly $$3 - 5\%$$, the textbook average being $$\approx 4\%$$.

Nature of exhaust (top) gas
The gases leaving the throat mainly contain $$CO$$ (≈ 30-35 %), $$N_2$$ (from blast air, ≈ 60-65 %) and a small amount of $$CO_2$$. Oxides of nitrogen such as $$NO_2$$ are not produced in any significant amount under the strongly reducing conditions of the furnace.

Option-wise verification

Option A: Limestone is used to remove silicate impurity.
Correct, because $$CaO$$ formed from limestone reacts with $$SiO_2$$ to give slag $$CaSiO_3$$.

Option B: Pig iron obtained from blast furnace contains about 4 % carbon.
Correct; the molten iron indeed contains roughly $$3 - 5\%$$ carbon.

Option C: Coke ($$C$$) converts $$CO_2$$ to $$CO$$.
Correct, via the Boudouard reaction $$C + CO_2 \rightarrow 2\,CO$$ which predominates between $$900 - 1500 \text{ K}$$.

Option D: Exhaust gases consist of $$NO_2$$ and $$CO$$.
Incorrect; the main constituents are $$CO$$ and $$N_2$$, not $$NO_2$$.

Hence the correct choices are
Option A (Limestone removes silicate impurity),
Option B (Pig iron contains ≈ 4 % C) and
Option C (Coke converts $$CO_2$$ to $$CO$$).

Option A, Option B and Option C are correct.