There are certain substances which behave as normal, strong electrolyte at low concentration but at higher concentration they behave as colloidal solutions due to the formation of aggeregated particles. Such colloidals called associated colloids and the aggeregated particles are called micelles. The formation of micelles take place above certain concentration called critical micelization concentration called critical micellization concentration (CMC) and a characteristic temperature.
Micelles are used in

Options

A. Detergents
B. Petroleum recovery
C. Magnetic separation
D. All of these

Answer

### Step-by-Step Solution:

1. **Understanding Micelles**: Micelles are formed by surfactant molecules when they aggregate above a certain concentration known as the Critical Micellization Concentration (CMC). At low concentrations, surfactants behave as normal strong electrolytes, but at higher concentrations, they form colloidal solutions due to the aggregation of particles.

2. **Composition of Surfactants**: Surfactants consist of two distinct parts: a hydrophobic (water-repelling) tail and a hydrophilic (water-attracting) head. This dual nature allows surfactants to interact with both water and oily substances.

3. **Formation of Micelles**: When surfactants are added to water and the concentration exceeds the CMC, the surfactant molecules arrange themselves into spherical structures called micelles. The hydrophobic tails point inward, away from the water, while the hydrophilic heads face outward, interacting with the water.

4. **Application of Micelles**: Micelles have practical applications, particularly in the field of cleaning. When used in detergents, micelles help to remove dirt and grease from surfaces. The hydrophobic tails of the surfactants attach to grease and dirt, while the hydrophilic heads remain in the water, allowing the dirt to be washed away.

5. **Conclusion**: Based on the properties and functions of micelles, they are primarily used in detergents for cleaning purposes. The micelles encapsulate dirt and grease, making it easier to rinse them away with water.

### Final Answer:
Micelles are used in detergents.

---