Which of the following is not a colloidal systems ?

Options

A. Blood
B. Steel
C. Fog
D. Foam

Answer

To determine which of the following is not a colloidal system, we need to understand the definition of a colloid. A colloid is a heterogeneous mixture where one substance (the dispersed phase) is finely dispersed in another substance (the dispersion medium).

### Step-by-Step Solution:

1. **Identify the Components of a Colloid:**
- A colloid consists of two main components:
- **Dispersed Phase:** The substance that is present in a smaller amount (similar to solute in a solution).
- **Dispersion Medium:** The substance that is present in a larger amount (similar to solvent in a solution).

2. **Examine the Options:**
- We need to analyze each option to see if it fits the definition of a colloidal system.

3. **Option 1: Blood**
- Blood is a colloidal system where:
- **Dispersion Medium:** Liquid (plasma)
- **Dispersed Phase:** Cells (solid particles)
- Conclusion: Blood is a colloidal system.

4. **Option 2: Steel**
- Steel is an alloy, which is a mixture of metals and does not fit the colloidal definition.
- Conclusion: Steel is not a colloidal system.

5. **Option 3: Fog**
- Fog is a colloidal system where:
- **Dispersion Medium:** Gas (air)
- **Dispersed Phase:** Liquid (water droplets)
- Conclusion: Fog is a colloidal system.

6. **Option 4: Foam**
- Foam is a colloidal system where:
- **Dispersion Medium:** Solid (the structure of the foam)
- **Dispersed Phase:** Gas (air bubbles)
- Conclusion: Foam is a colloidal system.

7. **Final Conclusion:**
- Among the options provided, only **Option 2: Steel** is not a colloidal system.

### Answer:
**Steel is not a colloidal system.**

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