Colloidal solutions of metals like gold, silver and platinum are generally prepared by using:

Options

A. peptization
B. Bredig's are method
C. Exchange of solvent
D. Oxidation method

Answer

To solve the question regarding the preparation of colloidal solutions of metals like gold, silver, and platinum, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Colloidal Solutions**:
- Colloidal solutions consist of tiny particles dispersed in a medium. In this case, we are looking at metals like gold, silver, and platinum.

2. **Identifying Preparation Methods**:
- There are various methods to prepare colloidal solutions, including peptization, the Bredig's arc method, and others. We need to identify which method is specifically used for the metals mentioned.

3. **Bredig's Arc Method**:
- The Bredig's arc method is a well-known technique for preparing colloidal solutions of metals. It involves the use of an electric arc.

4. **Process of Bredig's Arc Method**:
- **Striking the Arc**: An electric arc is struck between two electrodes that are immersed in a dispersion medium (like water).
- **Vaporization**: The intense heat generated by the electric arc vaporizes the metal.
- **Condensation**: The vaporized metal then condenses into small particles, forming a colloidal solution.

5. **Conclusion**:
- Based on the above steps, we conclude that the colloidal solutions of metals like gold, silver, and platinum are generally prepared using the Bredig's arc method.

### Final Answer:
The correct answer is the **Bredig's arc method**.

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