Which of the following is an example of a colloid?

Milk is indeed an example of a colloid. In a colloid, tiny particles are dispersed throughout a continuous medium but do not settle out like in a suspension. In the case of milk, fat globules are dispersed in water, creating an opaque mixture that retains some of the properties of both its liquid and solid components. The small size of the suspended fat globules prevents them from settling at the bottom and allows milk to appear homogeneous to the naked eye.

Saltwater and sugar solutions are examples of true solutions, where the solute completely dissolves in the solvent, resulting in a uniform mixture with particles at the molecular level that cannot scatter light. Vinegar, being a solution of acetic acid in water, also falls into this category and forms a true solution rather than a colloid. Thus, milk stands out as the correct choice for an example of a colloid among the provided options.