Which of the following can protect a gold sol from coagulation by NaCl solution?

Options

A. `Fe(OH)_(3)`
B. Gelatin
C. `As_(2)S_(3)`
D. None of these

Answer

To determine which substance can protect a gold sol from coagulation by NaCl solution, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Coagulation**:
- Coagulation is the process where colloidal particles aggregate and settle out of the solution. In this case, NaCl, being a strong electrolyte, can cause the gold sol to coagulate.

2. **Identifying Protective Colloids**:
- To prevent coagulation, we need to use a protective colloid. Protective colloids are substances that can stabilize colloidal systems against coagulation.

3. **Characteristics of Protective Colloids**:
- Protective colloids are typically leophilic colloids, which means they are solvent-loving and can interact favorably with the solvent, thus stabilizing the colloidal particles.

4. **Examples of Protective Colloids**:
- Common examples of leophilic colloids include gelatin and starch. These substances can effectively protect the gold sol from coagulation by providing a stabilizing effect.

5. **Conclusion**:
- Therefore, the correct answer to the question is gelatin, as it is a leophilic colloid that can protect the gold sol from coagulation by NaCl.

### Final Answer:
**Gelatin** can protect a gold sol from coagulation by NaCl solution.

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