A colloidal solution of arsenious sulphide is most readily coagulated by the addition of a normal solution?

Options

A. NaCl
B. `CaCI_(2)`
C. `Na_(3)PO_(4)`
D. `AI_(2)(SO_(4))_(3)`

Answer

To solve the question of which normal solution most readily coagulates a colloidal solution of arsenious sulfide (As₂S₃), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Nature of the Colloidal Solution:**
- Arsenious sulfide (As₂S₃) forms a colloidal solution that is negatively charged due to the presence of sulfide ions (S²⁻).

2. **Understand Coagulation:**
- Coagulation of colloidal solutions occurs when oppositely charged ions are added. Since As₂S₃ is negatively charged, it will be coagulated by positively charged ions (cations).

3. **Evaluate the Options:**
- We need to look at the provided options and identify the cations present in each normal solution:
- Option 1: Na⁺ (sodium ion)
- Option 2: Ca²⁺ (calcium ion)
- Option 3: Na⁺ (sodium ion)
- Option 4: Al³⁺ (aluminum ion)

4. **Determine Coagulating Power:**
- According to Hardy-Schulze rule, the coagulating power of a cation is directly related to its charge (valency). The higher the charge, the greater the coagulating power.
- Here are the charges of the cations:
- Na⁺ has a charge of +1
- Ca²⁺ has a charge of +2
- Al³⁺ has a charge of +3

5. **Select the Best Option:**
- Among the cations, Al³⁺ has the highest charge (+3), which means it has the greatest coagulating power.
- Therefore, the colloidal solution of arsenious sulfide will be most readily coagulated by the addition of Al₂(SO₄)₃ (aluminum sulfate).

### Conclusion:
The correct answer is **Option 4: Al₂(SO₄)₃**.

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