What is the main cause of charge on a colloidal solution?

Explanation

### Step-by-Step Solution:

1. **Understanding Colloidal Solutions**:
- A colloidal solution is a heterogeneous mixture where the particle size is intermediate between true solutions and suspensions. The particles in a colloid do not settle out upon standing and cannot be separated by ordinary filtration.

2. **Identifying the Cause of Charge**:
- The charge on colloidal particles is primarily due to the adsorption of ions from the surrounding medium, particularly from electrolytes. This process is known as "electrokinetic charging."

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