What characteristic is most useful in classifying the mixture?

If they can be separated into individual components.

Explanation:

There are two types of mixtures: heterogeneous and homogeneous. Heterogeneous mixtures are not uniform throughout their composition. The opposite of heterogeneous mixtures are homogenous mixtures. Homogenous mixtures are uniform throughout their composition. They are called solutions. The determining factor for classifying whether or not a mixture is homogeneous or heterogeneous is whether or not their composition is uniform throughout. In other words, can the mixture be separated into individual components or not?

An example of a heterogenous mixture is if there was a bucket with sand mixed with rocks. An example of a homogenous mixture is a cup of coffee. This cup of coffee is composed of brewed coffee, milk, and sugar. This becomes homogeneous when all of it is well mixed.