Which of the following is most effective in coagulating negatively charged hydrated ferric oxide sol?

Options

A. `NaNO_3`
B. `MgSO_4`
C. `AlCl_3`
D. `KCl`

Explanation

To determine which of the given cations is most effective in coagulating negatively charged hydrated ferric oxide sol, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Charge of the Colloid**:
- The hydrated ferric oxide sol is negatively charged.

2. **Understand the Coagulation Process**:
- Coagulation involves the neutralization of the charge on the colloidal particles. For negatively charged colloids, positively charged ions (cations) are required for coagulation.

3. **List the Given Cations**:
- The options provided are:
1. Na⁺ (Sodium ion)
2. Mg²⁺ (Magnesium ion)
3. Al³⁺ (Aluminum ion)
4. K⁺ (Potassium ion)

4. **Apply the Hardy-Schulze Rule**:
- According to the Hardy-Schulze rule, the coagulating power of a cation is directly proportional to its charge. This means that cations with higher positive charges will be more effective in coagulating negatively charged colloids.

5. **Compare the Charges of the Cations**:
- Na⁺ has a charge of +1.
- K⁺ has a charge of +1.
- Mg²⁺ has a charge of +2.
- Al³⁺ has a charge of +3.

6. **Determine the Most Effective Cation**:
- Since Al³⁺ has the highest charge (+3), it will be the most effective in coagulating the negatively charged hydrated ferric oxide sol, followed by Mg²⁺ (+2), and then Na⁺ and K⁺ (+1).

7. **Conclusion**:
- Therefore, the most effective cation for coagulating negatively charged hydrated ferric oxide sol is **Al³⁺ (Aluminum ion)**.

### Final Answer:
**Al³⁺ (Aluminum ion)** is the most effective in coagulating negatively charged hydrated ferric oxide sol.

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