Final answer:
A colloid is a mixture with particles sized between 2 to 500 nm that do not settle upon standing, which is intermediate between a solution (particle size < 2 nm) and a suspension (> 1000 nm).
Step-by-step explanation:
The type of mixture formed by particles that are intermediate in size between those in solutions and suspensions is known as a colloid. In colloids, the particle sizes range from about 2 to 500 nm. Examples include fog (liquid particles in a gas), milk (solid particles in a liquid), and butter (solid particles in a solid). Unlike suspensions, colloidal particles do not settle when left to stand and can't be separated from the dispersion medium by filtering. In contrast, solutions are homogeneous mixtures with particles size of ions or small molecules of about 0.1-2.0 nm, and suspensions are heterogeneous mixtures with particle sizes usually larger than 1000 nm that settle upon standing.