The dispersed phase in colloidal iron (III) hydroxide and collodial gold is positively and negtively charged respectively with of the following statement is not correct ?

Options

A. Magnesium chloride solution coagulates gold sol readily than iron (III) hydroxide sol.
B. Sodium sulphate solution causes coagulation in both sols.
C. Mixing of the two sols has no effect.
D. Coagulation in both sols can be brought about by electrophoresis.

Explanation

To solve the question regarding the dispersed phases in colloidal iron (III) hydroxide and colloidal gold, we will analyze the statements given and determine which one is not correct.

### Step-by-Step Solution:

1. **Identify the Charges of the Colloids**:
- Colloidal iron (III) hydroxide (Fe(OH)₃) is positively charged.
- Colloidal gold (Au) is negatively charged.

2. **Analyze the Statements**:
- **Statement 1**: "Magnesium chloride solution coagulates gold sol readily than iron (III) hydroxide sol."
- Magnesium chloride (MgCl₂) dissociates into Mg²⁺ and Cl⁻ ions. The Mg²⁺ ion has a +2 charge, which can effectively coagulate the negatively charged gold sol. Thus, this statement is correct.

- **Statement 2**: "Sodium sulfate solution causes coagulation in both sols."
- Sodium sulfate (Na₂SO₄) dissociates into 2Na⁺ and SO₄²⁻. The Na⁺ ions can coagulate the negatively charged gold sol, while the SO₄²⁻ ions can coagulate the positively charged iron (III) hydroxide sol. Therefore, this statement is also correct.

- **Statement 3**: "Mixing of two sols has no effect."
- When mixing a positively charged sol (iron (III) hydroxide) with a negatively charged sol (gold), mutual coagulation occurs. Therefore, this statement is incorrect, as mixing the two sols will lead to coagulation.

- **Statement 4**: "Coagulation in both sols can be brought about by electrophoresis."
- Electrophoresis involves applying an electric field to the colloidal solution, which causes the positively charged particles to move towards the negative electrode and vice versa. This process can indeed lead to coagulation in both sols. Thus, this statement is correct.

3. **Conclusion**:
- The statement that is not correct is **Statement 3**: "Mixing of two sols has no effect."

### Final Answer:
The statement that is not correct is: **"Mixing of two sols has no effect."**

---