Which of the following metal sols. cannot be prepared by Bredig’s arc method -

Options

A. Gold
B. Silver
C. Platinum
D. Sodium

Answer

To determine which of the following metal sols cannot be prepared by Bredig’s arc method, we first need to understand the Bredig’s arc method itself and the types of metals that can be used in this process.

### Step-by-Step Solution:

1. **Understanding Bredig’s Arc Method**:
- Bredig’s arc method is a technique used to prepare colloidal solutions of metals. It involves the use of an electrical arc to vaporize the metal, which then condenses into colloidal particles in a cold medium (usually water or ice).

2. **Common Metals Used**:
- The method is primarily effective for noble metals such as gold (Au), silver (Ag), and platinum (Pt). These metals have properties that allow them to form stable colloidal solutions.

3. **Identifying the Metals in the Options**:
- The question likely provides a list of metals. We need to identify which of these metals can or cannot be prepared using the Bredig’s arc method.

4. **Analyzing Each Metal**:
- **Gold (Au)**: Can be prepared using Bredig’s arc method.
- **Silver (Ag)**: Can be prepared using Bredig’s arc method.
- **Platinum (Pt)**: Can be prepared using Bredig’s arc method.
- **Sodium (Na)**: Cannot be prepared using Bredig’s arc method because sodium is a highly reactive alkali metal that does not form stable colloidal solutions in this manner.

5. **Conclusion**:
- Based on the analysis, the metal sol that cannot be prepared by Bredig’s arc method is **Sodium (Na)**.

### Final Answer:
**Sodium (Na)** cannot be prepared by Bredig’s arc method.