Lyophobic sols are:

Options

A. Reversible colloids
B. Irreversible colloids
C. Protective colloids
D. Gum proteins

Answer

### Step-by-Step Text Solution:

1. **Definition of Lyophobic Sols**:
- Lyophobic sols are colloidal systems where the dispersed phase (Dp) has little to no affinity for the dispersed medium (Dm). This lack of affinity means that these sols do not easily form or remain stable without special methods.

2. **Characteristics of Lyophobic Sols**:
- They are considered **irreversible colloids**. Once the dispersed phase precipitates (ppt), it cannot be easily re-dispersed into the medium without significant effort or the use of special techniques.
- Lyophobic sols do not form a protective layer around the dispersed particles, which contributes to their instability.

3. **Comparison with Lyophilic Sols**:
- In contrast, lyophilic sols have a good affinity between the dispersed phase and the medium, making them **reversible colloids**. If a lyophilic sol precipitates, it can be easily re-dispersed by simply shaking or adding more medium.
- Lyophilic sols tend to form protective layers around the dispersed particles, which enhances their stability.

4. **Examples of Lyophobic Sols**:
- Common examples of lyophobic sols include metals like gold (Au), silver (Ag), and certain sulfides (e.g., As2S3). These materials do not easily form stable colloidal solutions.

5. **Conclusion**:
- Therefore, lyophobic sols are characterized as irreversible colloids due to their lack of affinity for the dispersed medium and their inability to be re-dispersed once precipitated.

### Final Answer:
Lyophobic sols are **irreversible colloids**.

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