In Bredig's arc method some alkali is added because

Explanation

**Step-by-Step Solution:**

1. **Understanding Bredig's Arc Method**:
- Bredig's arc method is a technique used to produce colloidal solutions, particularly metal colloids. It involves the use of an electric arc to vaporize the metal in the presence of a solvent.

2. **Role of Alkali**:
- In this method, an alkali (which refers to a water-soluble base) is added to the system. The purpose of adding alkali is to stabilize the colloidal solution formed during the process.

3. **Stabilization of Colloids**:
- Colloidal particles tend to aggregate due to van der Waals forces. The addition of alkali helps to provide a charge to the particles, which increases the electrostatic repulsion between them. This prevents them from coming together and forming larger particles, thus stabilizing the colloid.

4. **Conclusion**:
- Therefore, the addition of alkali in Bredig's arc method is crucial for stabilizing the colloidal solution, ensuring that the particles remain dispersed and do not aggregate.

---