Sponge
Explanation
Colloids are heterogeneous systems classified based on the physical state of the dispersed phase (the substance being dissolved) and the dispersion medium (the substance in which it is dissolved). A Solid Foam is a specific type of colloid where a gas is dispersed within a solid medium.
Analysis of Options:
- Mud: Incorrect. Mud is classified as a Sol, where solid particles (dispersed phase) are suspended in a liquid (dispersion medium).
- Sponge: Correct. A sponge consists of air pockets (gas dispersed phase) trapped within a solid structure (solid dispersion medium). This classifies it as a Solid Foam.
- Face cream Face cream: Incorrect. Face cream is an Emulsion, formed by a liquid dispersed in another liquid.
- Milky glass Milky glass: Incorrect. Milky glass is a Solid Sol, where solid particles are dispersed within a solid medium.
Key Takeaway:
In colloidal chemistry, a Solid Foam is defined by the combination of a Gas (Dispersed Phase) and a Solid (Dispersion Medium). Common examples include pumice stone, foam rubber, and sponge.