Which one of the following impurities present in colloidal solution cannot be removed by electrodialysis?

Options

A. Sodium chloride
B. Potassium sulphate
C. Urea
D. Calcium chloride

Explanation

To solve the question of which impurity present in a colloidal solution cannot be removed by electrodialysis, we need to understand the principles of electrodialysis and the nature of the impurities involved.

### Step-by-Step Solution:

1. **Understanding Electrodialysis**:
- Electrodialysis is a process that uses an electric field to drive the movement of ions through a semi-permeable membrane. This process is effective for removing ionic impurities (electrolytes) from a solution.

2. **Identifying Types of Impurities**:
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