An example of a solid emulsion is

Analysis

The question asks for an example of a solid emulsion. To answer this, we must understand the classification of colloids based on the physical states of the dispersed phase and the dispersion medium.

Concept: Colloids

A colloid is a mixture where one substance of microscopically dispersed insoluble particles is suspended throughout another substance. They are classified by the state of the two components:

• Dispersed Phase: The substance being distributed (the "solute").
• Dispersion Medium: The substance in which the particles are distributed (the "solvent").

An emulsion is specifically a colloid where both the dispersed phase and the dispersion medium are liquids. However, a solid emulsion occurs when a liquid is dispersed within a solid medium.

Step-by-Step Solution

1. Analyze the options: • Butter: This is a classic example of a solid emulsion. It consists of tiny droplets of water (liquid) dispersed throughout a solid fat (solid). • Hair cream: This is typically a liquid-in-liquid emulsion (oil-in-water or water-in-oil). • Milk: This is a liquid-in-liquid emulsion (fat droplets dispersed in water). • Cod-liver oil: This is a liquid-in-liquid emulsion (often prepared as an emulsion for medicinal purposes).

2. Evaluate against the definition: Since a solid emulsion requires a liquid dispersed in a solid, butter fits this definition perfectly because it is water trapped inside a solid fat matrix.

3. Conclusion:

Exam Tip

To remember these easily, use this quick table:

• Liquid in Liquid = Emulsion (e.g., Milk, Mayonnaise)
• Liquid in Solid = Solid Emulsion (e.g., Butter, Cheese)
• Gas in Liquid = Foam (e.g., Whipped cream, Soda foam)
• Solid in Liquid = Sol (e.g., Paints, Mud)