The impurest form of iron is:

Options

A. Scrap iron
B. Wrought iron
C. Cast iron
D. Pig iron

Explanation

To determine the impurest form of iron, we need to understand the different forms of iron and their purity levels.

### Step-by-Step Solution:

1. **Identify the Forms of Iron**:
The common forms of iron include:
- Wrought Iron
- Cast Iron
- Pig Iron
- Steel

2. **Understand the Composition**:
- **Wrought Iron**: Contains very low carbon content (about 0.1-0.25%) and is considered very pure.
- **Cast Iron**: Contains a higher carbon content (about 2-4%) and is less pure than wrought iron but more pure than pig iron.
- **Steel**: Contains carbon content ranging from 0.2% to 2% and is a more refined form of iron.
- **Pig Iron**: Contains the highest carbon content, typically around 3-4.5%, along with other impurities such as sulfur, phosphorus, and silicon.

3. **Determine the Impurest Form**:
Since pig iron has the highest carbon content and contains various impurities, it is classified as the impurest form of iron.

4. **Conclusion**:
Therefore, the impurest form of iron is **Pig Iron**.

### Final Answer:
The impurest form of iron is **Pig Iron**.

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