The form of iron obtained from blast furnace is:

The question asks about the form of iron obtained directly from the blast furnace in the extraction process. Let us understand the process step by step.

In the extraction of iron, the blast furnace is used to reduce iron ores, such as hematite (Fe2O3), magnetite (Fe3O4), or siderite (FeCO3). The raw materials fed into the blast furnace include iron ore, coke (which acts as a reducing agent and fuel), and limestone (CaCO3, which acts as a flux to remove impurities).

Inside the blast furnace, several chemical reactions occur. First, coke burns in the preheated air to form carbon dioxide:

$$ C + O_2 \rightarrow CO_2 $$

This carbon dioxide then reacts with excess coke to form carbon monoxide, the primary reducing agent:

$$ CO_2 + C \rightarrow 2CO $$

The carbon monoxide reduces the iron ore in stages. For hematite (Fe2O3), the reduction proceeds as follows:

$$ Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2 $$

Alternatively, the reduction can occur stepwise:

$$ 3Fe_2O_3 + CO \rightarrow 2Fe_3O_4 + CO_2 $$

$$ Fe_3O_4 + CO \rightarrow 3FeO + CO_2 $$

$$ FeO + CO \rightarrow Fe + CO_2 $$

Simultaneously, limestone decomposes to quicklime (CaO) and carbon dioxide:

$$ CaCO_3 \rightarrow CaO + CO_2 $$

The quicklime then reacts with acidic impurities like silica (SiO2) to form slag (calcium silicate):

$$ CaO + SiO_2 \rightarrow CaSiO_3 $$

The molten iron produced collects at the bottom of the blast furnace. This iron is not pure; it contains about 4-5% carbon, along with other impurities such as silicon, manganese, sulfur, and phosphorus. This high-carbon iron is called pig iron.

Now, let us examine the options:

• Option A: Cast Iron - This is produced by remelting pig iron and adjusting its composition. It has a lower carbon content (2-4%) than pig iron and is more refined.
• Option B: Wrought Iron - This is a highly refined form of iron with very low carbon content (less than 0.1%). It is made by further processing pig iron in a puddling furnace.
• Option C: Steel - This is an alloy of iron and carbon (typically 0.2-2.1% carbon), produced by reducing the carbon content of pig iron through processes like the Bessemer converter or open-hearth furnace.
• Option D: Pig Iron - This is the direct product of the blast furnace, characterized by high carbon content and impurities.

Since the blast furnace yields pig iron directly, the correct answer is Option D.

Hence, the correct answer is Option D.