Which of the following act as a protective colloids?

Options

A. Gelatin
B. Silica gel
C. Oil-in-water emulsion
D. All correct

Answer

To determine which of the given options acts as a protective colloid, we can analyze each option based on the definition of protective colloids.

### Step-by-Step Solution:

1. **Understand Protective Colloids**:
Protective colloids are typically lyophilic colloids that stabilize lyophobic colloids. They prevent the coagulation of lyophobic colloids when electrolytes are added. Examples of protective colloids include gelatin, natural gums, and cellulose derivatives.

2. **Evaluate the Options**:
- **Option 1: Gelatin**: Gelatin is a well-known protective colloid. It is a lyophilic colloid that can stabilize lyophobic colloids by preventing their coagulation.
- **Option 2: Silica Gel**: Silica gel is generally considered a desiccant and does not function as a protective colloid. It is a lyophobic colloid and does not stabilize other colloids.
- **Option 3: Oil in Water Emulsion**: This is a type of emulsion rather than a protective colloid. While emulsions can be stabilized by emulsifiers, they do not fit the definition of protective colloids.
- **Option 4: All Correct**: This option suggests that all previous options are protective colloids, which is not true based on our analysis.

3. **Conclusion**:
Based on the evaluation, the only protective colloid among the options provided is **gelatin**.

### Final Answer:
The correct answer is **gelatin**.