The method usually employed for the precipitation of a colloidal solution is

Options

A. dialysis
B. addition of electrolytes
C. diffusion through animal membrane
D. condensation

Answer

To solve the question regarding the method usually employed for the precipitation of a colloidal solution, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Colloidal Solutions**:
- Colloidal solutions consist of tiny particles dispersed in a medium. These particles can carry a charge, which helps keep them suspended in the solution.

2. **Identifying Precipitation Methods**:
- We need to evaluate the given options for methods that can lead to the precipitation of colloidal particles.

3. **Analyzing the Options**:
- **Dialysis**: This method involves the separation of colloidal particles from smaller solute particles through a semi-permeable membrane. It does not lead to precipitation.
- **Addition of Electrolyte**: When an electrolyte is added to a colloidal solution, it can neutralize the charge on the colloidal particles. This leads to aggregation of the particles, resulting in precipitation.
- **Diffusion through Animal Membrane**: Similar to dialysis, this method involves movement of particles and does not directly cause precipitation of colloidal solutions.
- **Condensation**: This refers to the process of forming colloids from vapors or gases, but it is not a method for precipitating existing colloidal solutions.

4. **Conclusion**:
- The most effective and commonly used method for precipitating colloidal solutions is the **addition of electrolyte**. This method causes the charged particles to neutralize and aggregate, leading to precipitation.

### Final Answer:
The method usually employed for the precipitation of a colloidal solution is **addition of electrolyte**.

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