Bredig's arc method cannot be used for the preparation of colloidal sol of :

Options

A. copper
B. gold
C. silver
D. sodium

Answer

To solve the question regarding Bredig's arc method and its applicability for preparing colloidal sols, we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding Bredig's Arc Method**:
- Bredig's arc method is a technique used to prepare colloidal solutions (sols) of metals. It involves creating an electric arc between two electrodes submerged in a liquid medium, which leads to the formation of metal colloids.

2. **Identifying Suitable Metals**:
- The method is typically suitable for metals that can be vaporized and condensed into colloidal particles. Common examples include noble metals like gold, silver, and copper.

3. **Analyzing the Options**:
- **Option 1: Copper** - Copper can be prepared using Bredig's arc method, as it is a metal that can form colloids.
- **Option 2: Gold** - Gold is also suitable for this method and is commonly prepared using Bredig's arc method.
- **Option 3: Silver** - Silver can be effectively prepared as a colloidal sol using this method.
- **Option 4: Sodium** - Sodium is a highly reactive alkali metal. It reacts vigorously with water and cannot be used in the Bredig's arc method, as it would not form a stable colloidal sol.

4. **Conclusion**:
- Based on the analysis, the metal that cannot be prepared using Bredig's arc method is Sodium. Therefore, the correct answer is **Option 4: Sodium**.

### Final Answer:
Bredig's arc method cannot be used for the preparation of colloidal sol of Sodium.