Which of the following is not a lyophilic colloid ?

Options

A. Milk
B. Gum
C. Fog
D. Blood

Answer

To determine which of the following is not a lyophilic colloid, we first need to understand what a lyophilic colloid is.

### Step-by-Step Solution:

1. **Definition of Lyophilic Colloids**:
- Lyophilic colloids are colloidal systems that are formed by mixing a substance (the dispersed phase) with a suitable dispersion medium (the continuous phase). They are stable and can be easily separated by physical methods such as evaporation.

2. **Characteristics of Lyophilic Colloids**:
- They are stable and reversible. This means that they can revert back to their original state after the dispersion medium is removed.
- Examples include substances like gum, gelatin, starch, and rubber.

3. **Identifying the Options**:
- The question provides options: milk, gum, fog, and blood.
- We need to analyze each option to see if it fits the definition of a lyophilic colloid.

4. **Analysis of Each Option**:
- **Milk**: Milk is an emulsion and is not easily separated into its components by physical means. Therefore, it is not a lyophilic colloid.
- **Gum**: Gum is a classic example of a lyophilic colloid; it is stable and can be separated by physical methods.
- **Fog**: Fog is an aerosol and is not considered a lyophilic colloid.
- **Blood**: Blood is a complex suspension and is also not a lyophilic colloid.

5. **Conclusion**:
- Based on the analysis, the options that are not lyophilic colloids include milk, fog, and blood. However, the question specifically asks for one option that is not a lyophilic colloid. The most straightforward answer is **milk**.

### Final Answer:
- **Milk** is not a lyophilic colloid.