Following is used as a reducing agent in metallurgy i.e. extraction of metals in blast furnace.

Options

A. carbon dioxide
B. carbon monoxide
C. graphite
D. soot

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which substance is used as a reducing agent in metallurgy, specifically in the extraction of metals in a blast furnace.

2. **Identifying the Options**: The options given are:
- Carbon Dioxide (CO₂)
- Carbon Monoxide (CO)
- Graphite
- Soot

3. **Analyzing Each Option**:
- **Carbon Dioxide (CO₂)**: In carbon dioxide, the oxidation state of carbon is +4. Since it is already in its highest oxidation state, it cannot act as a reducing agent (which would require it to be oxidized further).
- **Carbon Monoxide (CO)**: Carbon monoxide has a lower oxidation state (+2) and can act as a reducing agent. It can donate electrons to reduce metal ores.
- **Graphite**: Graphite is a form of carbon and is not typically used directly as a reducing agent in metallurgy.
- **Soot**: Soot is also a form of carbon and is not used as a reducing agent in metallurgy.

4. **Conclusion**: The only viable reducing agent among the options is Carbon Monoxide (CO).

5. **Explanation of the Process**: In a blast furnace, coke (a form of carbon) is burned in a limited supply of oxygen to produce carbon monoxide. This carbon monoxide then reduces iron ore (like hematite, Fe₂O₃) through a series of reactions:
- First, Fe₂O₃ is reduced to Fe₃O₄ by CO.
- Then, Fe₃O₄ is further reduced to FeO.
- Finally, FeO is reduced to iron (Fe) while CO is oxidized to CO₂.

6. **Final Answer**: Therefore, the correct answer to the question is **Carbon Monoxide (CO)**.

---