Which of the following sols is hydrophobic ?

Options

A. Gelatin
B. Gum
C. Starch
D. Sulphur

Answer

To determine which of the following sols is hydrophobic, we need to understand the definitions of hydrophobic and hydrophilic colloids.

### Step-by-Step Solution:

1. **Define Hydrophobic and Hydrophilic Colloids:**
- **Hydrophobic Colloids:** These are colloidal systems where the dispersion medium is water, and the dispersed phase does not have an affinity for water. They do not mix well with water.
- **Hydrophilic Colloids:** These are colloidal systems that have a strong affinity for water and can easily mix or dissolve in it.

2. **Analyze the Options:**
- **Option 1: Gelatin**
- Gelatin is known to be hydrophilic as it readily mixes with water. Therefore, this option is incorrect.
- **Option 2: Gum**
- Gum is also hydrophilic and can dissolve in water. Thus, this option is incorrect.
- **Option 3: Starch**
- Starch is another hydrophilic substance that can mix with water. Hence, this option is incorrect.
- **Option 4: Sulphur**
- Sulphur does not mix with water and does not form a colloidal solution when added to water. Therefore, it is classified as a hydrophobic colloid.

3. **Conclusion:**
- Based on the analysis of the options, the hydrophobic sol among the given choices is **sulphur**.

### Final Answer:
The hydrophobic sol is **sulphur**.