Which of the following electrolytes will not be most effective in the coagulation of fold sol?

Options

A. `NaNO_(3)`
B. `K_(4)[Fe(CN)_(6)]`
C. `Na_(3)PO_(4)`
D. `MgCl_(2)`

Explanation

To determine which electrolyte will not be the most effective in the coagulation of gold sol, we need to analyze the given options based on their cations and their ability to coagulate negatively charged colloids like gold sol.

### Step-by-Step Solution:

1. **Understand the Concept of Coagulation**:
- Coagulation is the process where colloidal particles aggregate to form larger particles, leading to precipitation. For a negatively charged sol like gold sol, we need a cationic coagulant to neutralize the negative charge.

2. **Identify the Given Electrolytes**:
- The given electrolytes are:
- NaNO3
- K4FeCN6
- Na3PO4
- MgCl2

3. **Determine the Cations of Each Electrolyte**:
- For NaNO3, the cation is Na⁺.
- For K4FeCN6, the cation is K⁺.
- For Na3PO4, the cation is Na⁺.
- For MgCl2, the cation is Mg²⁺.

4. **Evaluate the Cationic Valency**:
- Na⁺ has a valency of 1.
- K⁺ has a valency of 1.
- Mg²⁺ has a valency of 2.
- The cations Na⁺ and K⁺ have lower valency compared to Mg²⁺.

5. **Apply Hardy-Schulze Rule**:
- According to Hardy-Schulze law, the coagulation power is directly proportional to the valency of the ion. Higher the valency, more effective the coagulation.
- Therefore, Mg²⁺ (valency 2) will be the most effective in coagulating gold sol.

6. **Identify the Least Effective Electrolyte**:
- Since Mg²⁺ is the most effective, we need to identify which of the other cations (Na⁺ or K⁺) is less effective. Both Na⁺ and K⁺ have the same valency of 1, making them less effective than Mg²⁺.
- Thus, NaNO3 and Na3PO4 (both containing Na⁺) and K4FeCN6 (containing K⁺) will not be as effective as Mg²⁺.

7. **Conclusion**:
- The question asks for the electrolyte that will not be the most effective in coagulating gold sol. Therefore, the correct answer is any of the options containing Na⁺ or K⁺, as they are less effective compared to Mg²⁺.

### Final Answer:
The electrolytes NaNO3, K4FeCN6, and Na3PO4 will not be the most effective in the coagulation of gold sol.