Colloids represent a state of ……………..and not a class of substances.

Answer

**Step-by-Step Solution:**

1. **Understanding Colloids**: Colloids are defined as mixtures where the particle size ranges from 1 to 1000 nanometers. This range is crucial in distinguishing colloids from other types of mixtures, such as solutions and suspensions.

2. **Characteristics of Colloids**: Colloids exhibit unique properties, such as the Tyndall effect, where light is scattered by the colloidal particles. This is a key feature that helps identify colloidal systems.

3. **Behavior Under Different Conditions**: Colloids can behave differently depending on the medium they are in. For instance, sodium chloride (common salt) behaves as a colloid when dissolved in water but may act as a crystalloid in a non-polar solvent like benzene. This variability indicates that colloids are not a fixed class of substances but rather a state of a system.

4. **Conclusion**: Given that colloids can change their behavior based on conditions and are defined by their particle size, we conclude that colloids represent a "state of substance" rather than a specific class of substances.

5. **Final Answer**: Colloids represent a state of **substance** and not a class of substances.

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