Question

What is an example of a colloid?

Answer 1

There's actually 8 classes of colloid.....

Explanation:

1: Liquid in gas (e.g. fog)
2: Solid in gas (e.g smoke)
3: Gas in liquid (e.g. canned shaving cream)
4: Liquid in liquid (e.g. milk)
5: Solid in liquid (e.g. ink containing dispersed pigment)
6: Gas in solid (e.g. expanded polystyrene)
7: Liquid in solid (e.g. Jello)
8: Solid in solid (e.g. coloured glass).

In general terms you can't have a "gas in gas" colloid because gasses are fully miscible in all proportions as a single phase.

They key point is that in each case the system must be stable, it shouldnt separate into distinct phases on standing, and the dispersed phase should comprise particles whose mean size falls within the range of 1 and 1000 nm.