What happens:
(a) By persistent dialysis of a sol .

Explanation

**Step-by-Step Solution:**

1. **Understanding Dialysis**: Dialysis is a process that separates small solute particles from larger particles in a solution using a semi-permeable membrane. In the case of colloidal solutions, this process can be used to remove electrolytes.

2. **Role of Electrolytes in Colloidal Stability**: Colloidal solutions are stabilized by the presence of small amounts of electrolytes. These electrolytes help to maintain the repulsive forces between the colloidal particles, preventing them from aggregating or coagulating.

3. **Effect of Persistent Dialysis**: When persistent dialysis is carried out on a colloidal solution, the electrolytes present in the solution are gradually removed. This removal continues until the concentration of electrolytes is significantly reduced or eliminated.

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