The process of removal of impurities from a crude metal is called :

Options

A. concentration
B. calcination
C. refining
D. roasting

Explanation

To answer the question regarding the process of removal of impurities from a crude metal, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Crude Metal**:
- Crude metal is the initial form of metal extracted from ores, which contains various impurities and other unwanted materials.

2. **Definition of Refining**:
- The process of removing these impurities to obtain a purer form of the metal is known as "refining."

3. **Methods of Refining**:
- Refining can be achieved through various methods, which can be categorized as:
- **Physical Methods**: These involve physical processes such as filtration or sedimentation to separate impurities based on their physical properties.
- **Chemical Methods**: These involve chemical reactions to remove impurities, such as using acids or other reagents.
- **Electrolytic Refining**: This is a specific method where an electric current is used to deposit pure metal from a solution onto an electrode.

4. **Purity of Refined Metal**:
- After refining, the metal obtained is not 100% pure but is usually around 99.9% pure, which is sufficient for most applications.

5. **Conclusion**:
- Therefore, the answer to the question is that the process of removal of impurities from a crude metal is called **refining**.