Which of the following substance gives a positively charged sol?

Options

A. Gold
B. Arsenious sulphide`|S^(2-)`
C. Ferric hydroxide
D. Soap

Answer

To determine which of the given substances gives a positively charged sol, we can analyze each option based on their properties and behavior in a colloidal system.

### Step-by-Step Solution:

1. **Identify the Options**: The options provided are:
- Gold
- Arsenious Sulphide (As₂S₃)
- Ferric Hydroxide (Fe(OH)₃)
- Silica

2. **Analyze Gold Sol**:
- Gold sols are typically prepared using reduction methods.
- When gold is dispersed in a sol, it tends to adsorb negatively charged ions (like AuO₂⁻).
- Therefore, gold sol gives a negatively charged sol.
- **Conclusion**: Gold does not give a positively charged sol.

3. **Analyze Arsenious Sulphide (As₂S₃)**:
- Arsenious sulphide dissociates into positive (As₃⁺) and negative (S²⁻) ions.
- The presence of positively charged ions means that the sol will attract negative ions, leading to a negatively charged sol.
- **Conclusion**: Arsenious sulphide does not give a positively charged sol.

4. **Analyze Ferric Hydroxide (Fe(OH)₃)**:
- Ferric hydroxide is formed by the reaction of ferric chloride with a base.
- It dissociates into Fe³⁺ and OH⁻ ions.
- Ferric hydroxide tends to adsorb positive Fe³⁺ ions, leading to the formation of a positively charged sol.
- **Conclusion**: Ferric hydroxide gives a positively charged sol.

5. **Analyze Silica**:
- Silica (SiO₂) in a neutral pH environment typically remains uncharged, but it can form negatively charged sols under certain conditions.
- Therefore, silica does not give a positively charged sol.
- **Conclusion**: Silica does not give a positively charged sol.

### Final Answer:
The substance that gives a positively charged sol is **Ferric Hydroxide (Fe(OH)₃)**.

---