Which of the following is not a method for coagulation of lyophobic sols ?

Options

A. By electrophoresis
B. By mixing oppositely charged sols
C. By adding electrolyte
D. By adding a protective colloid

Explanation

To determine which of the following is not a method for the coagulation of lyophobic sols, we will analyze each option provided:

1. **Electrophoresis**: This method involves the movement of charged particles in a fluid under the influence of an electric field. In the case of lyophobic sols, electrophoresis can lead to the coagulation of particles as they migrate towards the oppositely charged electrode, allowing them to aggregate. Thus, this is a valid method for coagulation.

2. **Mixing oppositely charged sols**: When lyophobic sols with opposite charges are mixed, they can neutralize each other’s charges, leading to coagulation. This is a common method used to induce coagulation in colloidal systems. Therefore, this is also a valid method for coagulation.

3. **Adding electrolytes**: The addition of electrolytes to a lyophobic sol can lead to coagulation by neutralizing the charges on the colloidal particles, allowing them to come together and form larger aggregates. This is a well-known method for coagulating lyophobic sols.

4. **Adding protective colloids**: Protective colloids are substances that stabilize lyophobic sols by forming a protective layer around the particles. Instead of causing coagulation, they actually increase the stability of lyophobic sols. Therefore, adding protective colloids does not lead to coagulation but rather prevents it.

Based on this analysis, the method that is not used for coagulation of lyophobic sols is:

**Answer: Adding protective colloids.**