Which of the following ions has the maximum flocculation value towards coagulation of a positive sol?

Options

A. `[Fe(CN)_(6))]^(4-)`
B. `CI^(-)`
C. `SO_(4)^(2-)`
D. `PO_(4)^(3-)`

Answer

To determine which ion has the maximum flocculation value towards the coagulation of a positive sol, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Flocculation Value**:
- The flocculation value is defined as the minimum concentration of an electrolyte required to cause the coagulation (or flocculation) of a colloidal solution (sol).

2. **Hardy-Schulze Rule**:
- According to the Hardy-Schulze rule, the flocculation value is inversely proportional to the coagulating power of the ion. This means that ions with higher valency will have a lower flocculation value, and ions with lower valency will have a higher flocculation value.

3. **Coagulating Power**:
- The coagulating power of an ion is directly related to its valency. Therefore, for a positive sol, we need to consider negatively charged ions (anions) for coagulation.

4. **Analyzing the Given Ions**:
- Let's analyze the given anions based on their charges:
- CN⁻ (charge -1)
- SO₄²⁻ (charge -2)
- PO₄³⁻ (charge -3)
- CN₆⁴⁻ (charge -4)

5. **Determining Valency**:
- The valency of each ion is as follows:
- CN⁻: 1
- SO₄²⁻: 2
- PO₄³⁻: 3
- CN₆⁴⁻: 4

6. **Comparing Flocculation Values**:
- According to the Hardy-Schulze rule, the ion with the lowest valency will have the highest flocculation value. Therefore, we can arrange the ions in order of increasing valency and decreasing flocculation value:
- CN⁻ (highest flocculation value)
- SO₄²⁻
- PO₄³⁻
- CN₆⁴⁻ (lowest flocculation value)

7. **Conclusion**:
- From the analysis, CN⁻ has the maximum flocculation value towards the coagulation of a positive sol.

### Final Answer:
The ion with the maximum flocculation value towards coagulation of a positive sol is **CN⁻**.