What type of mixture can easily separate into layers over time?

A suspension is a type of mixture where solid particles are dispersed in a liquid or gas but are not dissolved. Over time, the solid particles in a suspension will settle out due to gravity, leading to the formation of distinct layers. This property is a result of the particles being larger than those in colloids or solutions, which allows them to settle when left undisturbed.

In contrast, a colloid consists of tiny particles that do not settle out upon standing, resulting in a uniform appearance. A solution is a homogeneous mixture where one substance is completely dissolved in another, and it does not separate into layers. Homogeneous mixtures are uniform in composition and do not show distinct layers upon standing, as all components are evenly distributed throughout. These characteristics make suspensions unique, as they distinctly separate into layers over time, confirming that it is the correct choice.