Which of the following has least coagluating value for positive sol ?

Options

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

Answer

To determine which of the given ions has the least coagulating value for a positive sol, we need to understand the concept of coagulation in colloidal chemistry.

### Step-by-Step Solution:

1. **Understanding Coagulation**: Coagulation is the process where colloidal particles aggregate to form a larger mass. For a positive sol (which has a positive charge), we need negatively charged ions to neutralize the charge and facilitate coagulation.

2. **Identifying the Ions**: The ions given in the options are:
- Cl⁻ (Chloride)
- SO₄²⁻ (Sulfate)
- PO₄³⁻ (Phosphate)
- Fe(CN)₆⁴⁻ (Ferricyanide)

3. **Valency of the Ions**: The coagulating power of an ion is inversely related to its valency. The higher the negative charge (valency), the greater the coagulating power. Here are the valencies for the ions:
- Cl⁻: Valency = 1
- SO₄²⁻: Valency = 2
- PO₄³⁻: Valency = 3
- Fe(CN)₆⁴⁻: Valency = 4

4. **Comparing Coagulating Values**: Since coagulating power increases with the negative charge:
- Cl⁻ (Valency 1) has the least coagulating power.
- SO₄²⁻ (Valency 2) has more coagulating power than Cl⁻.
- PO₄³⁻ (Valency 3) has even more coagulating power.
- Fe(CN)₆⁴⁻ (Valency 4) has the highest coagulating power.

5. **Conclusion**: Since Cl⁻ has the lowest valency, it has the least coagulating value for a positive sol.

### Final Answer:
The ion with the least coagulating value for a positive sol is **Cl⁻ (Chloride)**.

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