The disadvantage of carbon reduction method are :

Options

A. high temperature needed which is expensive and requires the use of a blast furnace
B. many metals combine with carbon forming carbides
C. carbon combines with oxgen to form poisonous CO
D. carbon cannot be used with highly electropositive metals

Answer

### Step-by-Step Solution:

1. **Understanding Carbon Reduction Method**:
- The carbon reduction method is a metallurgical process used to extract metals from their ores. In this process, carbon is used to reduce metal oxides to metals.

2. **Identifying Disadvantages**:
- While the carbon reduction method is effective, it has several disadvantages that need to be considered.

3. **High Temperature Requirement**:
- The process requires very high temperatures, which can be costly. This necessitates the use of blast furnaces, leading to increased operational costs.

4. **Formation of Metal Carbides**:
- During the reduction process, some metals can react with carbon to form metal carbides. This can result in a loss of the desired metal and can complicate the purification process.

5. **Production of Carbon Monoxide**:
- The reaction between carbon and oxygen can produce carbon monoxide (CO), which is a toxic gas. Although industrial plants often have systems to manage CO emissions, it remains a significant environmental concern.

6. **Limitations with Highly Electropositive Metals**:
- Carbon reduction is not suitable for highly electropositive metals (like sodium or potassium) because these metals cannot be effectively reduced using carbon due to their strong affinity for oxygen.

7. **Conclusion**:
- The main disadvantages of the carbon reduction method include:
- High temperature requirements leading to increased costs.
- Formation of metal carbides.
- Production of poisonous carbon monoxide.
- Incompatibility with highly electropositive metals.

### Summary of Disadvantages:
- **High temperature needed**: Expensive and requires blast furnaces.
- **Formation of carbides**: Many metals can combine with carbon to form carbides.
- **Toxic by-products**: Carbon can combine with oxygen to form poisonous CO.
- **Limitations with certain metals**: Carbon cannot be used with highly electropositive metals.