Mutual coagulation is done by:

Options

A. Persistent dialysis
B. Electrophoresis
C. Mixing of two sols with opposite charge
D. Ultrafiltration method

Answer

To solve the question "Mutual coagulation is done by:", we need to understand the concept of mutual coagulation in colloidal chemistry.

### Step-by-Step Solution:

1. **Understanding Mutual Coagulation**:
- Mutual coagulation refers to the process where two oppositely charged colloidal particles are mixed together. When these particles are mixed in equimolar proportions, they neutralize each other's charges.

2. **Example of Mutual Coagulation**:
- A classic example is when a positively charged colloid, such as Fe(OH)3, is mixed with a negatively charged colloid, such as As2S3. The opposite charges cause them to coagulate or precipitate out of the solution.

3. **Analyzing the Options**:
- **Option 1**: Persistent Dialysis - This process involves removing electrolytes from a colloidal solution, leading to instability and coagulation, but it is not mutual coagulation.
- **Option 2**: Electrophoresis - This refers to the movement of charged colloidal particles in an electric field, which is not related to mutual coagulation.
- **Option 3**: Mixing of two sols with opposite charge - This is the correct definition of mutual coagulation.
- **Option 4**: Ultra Filtration - This method is used to purify colloidal solutions but does not involve mutual coagulation.

4. **Conclusion**:
- Based on the analysis, the correct answer to the question "Mutual coagulation is done by" is **Option 3: Mixing of two sols with opposite charge**.