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)

The correct options related to the extraction of iron from its ore in the blast furnace operating in the temperature range 900 - 1500 K are:
• Limestone is used to remove silicate impurity.
• Pig iron obtained from blast furnace contains about 4% carbon.
• Coke (C) converts CO₂ to CO.

Let us analyze each statement based on the chemical reactions and conditions inside the blast furnace during the extraction of iron:

1. Role of Limestone (CaCO₃):
In the temperature range of 900 - 1500 K, limestone undergoes thermal decomposition to form calcium oxide (CaO) and carbon dioxide (CO₂):

${\text{CaCO}}_3\to \text{CaO}+{\text{CO}}_2$

Calcium oxide acts as a basic flux and reacts with silica (silicate impurity, SiO₂) present in the ore to form calcium silicate slag (CaSiO₃):

$\text{CaO}+{\text{SiO}}_2\to {\text{CaSiO}}_3$

This slag melts and floats over the molten iron, allowing easy removal of silicate impurities. Hence, this option is correct.

2. Carbon Content in Pig Iron:
The iron obtained directly from the bottom of the blast furnace is known as pig iron. It contains about 4% carbon along with minor impurities such as S, P, Si, and Mn. Thus, this option is correct.

3. Reduction of CO₂ by Coke:
In the temperature range of 900 - 1500 K, carbon dioxide gas reacts with hot coke (C) to form carbon monoxide (CO), which acts as the main reducing agent in the furnace:

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

Hence, Coke (C) converts CO₂ to CO, making this option correct.

4. Composition of Exhaust Gases:
The exhaust gases escaping from the top of the blast furnace mainly consist of CO, CO₂, and N₂ (from air). They do not contain significant amounts of NO₂. Therefore, this option is incorrect.