Which of the following is an example of a colloid?

A colloid is a mixture where very small particles of one substance are dispersed in another substance. In a colloid, the dispersed particles are not large enough to settle out or be easily separated by filtration, and they typically remain suspended throughout the medium.

Milk is an excellent example because it contains fat globules and proteins dispersed in water. This creates a heterogeneous mixture that exhibits properties of both a solution and a suspension, allowing it to maintain a stable appearance while still being a colloidal mixture.

In contrast, saltwater is a true solution where the salt dissolves completely in water and the resulting mixture is homogenous. Sand is a solid that does not mix with water, resulting in a heterogeneous mixture where the sand settles at the bottom, and vinegar, while a homogenous solution of acetic acid in water, does not contain the dispersed particles characteristic of a colloid.