What is true about associated colloids?

Options

A. These consist of aggregate of atoms and molecules with diameter less than 1 nm
B. These are substances which behave like colloids only at higher concentration
C. These are substances which behave like colloids only at lower temperature
D. None of these

Answer

### Step-by-Step Solution:

1. **Definition of Associated Colloids**:
- Associated colloids are substances that behave as normal electrolytes at low concentrations but exhibit colloidal behavior at higher concentrations due to the formation of aggregates or clusters.

2. **Formation of Aggregates**:
- The colloidal behavior of associated colloids arises from the formation of aggregates, which are larger particles formed when the concentration of the substance increases.

3. **Terminology**:
- The aggregated particles formed in this process are referred to as "micelles."

4. **Critical Conditions**:
- The formation of micelles occurs above a specific temperature known as the Kraft temperature and above a certain concentration referred to as the critical micelle concentration (CMC).

5. **Examples**:
- Common examples of associated colloids include soaps and synthetic detergents.

6. **Evaluation of Options**:
- **Option 1**: "These consist of aggregate of atom and molecule with diameter less than 1 nanometer."
- This is incorrect as associated colloids form larger particles at higher concentrations.
- **Option 2**: "These are the substances which behave like colloid only at higher concentration."
- This is correct because associated colloids exhibit colloidal properties primarily at higher concentrations.
- **Option 3**: "These are the substances which behave like colloid only at low temperature."
- This is incorrect as associated colloids behave like colloids at higher concentrations, not specifically at low temperatures.
- **Option 4**: (not specified in the transcript, but can be assumed incorrect based on previous evaluations).

7. **Conclusion**:
- The correct statement about associated colloids is that they behave like colloids only at higher concentrations due to the formation of aggregates.