Which one of the following acts as the best coagulating agent for ferric hydroxide sol?

Options

A. Potassium ferrocyanide
B. Potassium chloride
C. Potassium oxalate
D. Aluminium chloride

Explanation

To determine the best coagulating agent for ferric hydroxide sol (Fe(OH)₃), we need to analyze the options provided and identify which one has the highest number of negatively charged ions. Ferric hydroxide is a positively charged colloid, and to coagulate it, we need a negatively charged agent that can neutralize its charge.

### Step-by-Step Solution:

1. **Identify the Charge of Ferric Hydroxide Sol**:
- Ferric hydroxide (Fe(OH)₃) is a positively charged sol. This means that to coagulate it, we need a negatively charged ion or electrolyte.

2. **List the Given Coagulating Agents**:
- The options provided are:
- Potassium Ferrocyanide (K₄[Fe(CN)₆])
- Potassium Chloride (KCl)
- Potassium Oxalate (K₂C₂O₄)
- Aluminum Chloride (AlCl₃)

3. **Analyze Each Coagulating Agent**:
- **Potassium Ferrocyanide (K₄[Fe(CN)₆])**:
- This compound can be dissociated into K⁺ and [Fe(CN)₆]⁴⁻.
- The anion [Fe(CN)₆]⁴⁻ has 4 negative charges.

- **Potassium Chloride (KCl)**:
- This dissociates into K⁺ and Cl⁻.
- Cl⁻ has only 1 negative charge.

- **Potassium Oxalate (K₂C₂O₄)**:
- This dissociates into K⁺ and C₂O₄²⁻.
- C₂O₄²⁻ has 2 negative charges.

- **Aluminum Chloride (AlCl₃)**:
- This dissociates into Al³⁺ and Cl⁻.
- There are 3 Cl⁻ ions, contributing a total of 3 negative charges.

4. **Compare the Number of Negative Charges**:
- Potassium Ferrocyanide: 4 negative charges
- Potassium Chloride: 1 negative charge
- Potassium Oxalate: 2 negative charges
- Aluminum Chloride: 3 negative charges

5. **Determine the Best Coagulating Agent**:
- Since the goal is to find the best coagulating agent, we need the one with the highest number of negative charges.
- Potassium Ferrocyanide has 4 negative charges, which is the highest among the options.

6. **Conclusion**:
- Therefore, the best coagulating agent for ferric hydroxide sol is **Potassium Ferrocyanide (K₄[Fe(CN)₆])**.

### Final Answer:
**Potassium Ferrocyanide (K₄[Fe(CN)₆]) acts as the best coagulating agent for ferric hydroxide sol.**