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 "Which one of the following impurities present in colloidal solution cannot be removed by electrodialysis?", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Electrodialysis**:
- Electrodialysis is a method used for the purification of colloidal solutions. It involves the movement of ions towards oppositely charged electrodes (anode and cathode).

2. **Identifying the Mechanism**:
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