explain the differences between the particles of a pure substance and the particles of a mechanical mixture

A substance is pure if it is a single substance, and it is made up of only one type of particle. If there is more than one substance, and therefore more than one type of particle, it is a mechanical mixture, the particles can be easily distinguished, due to their non-uniform composition. The composition of a mechanical mixture is variable and their components may be separated by physical or mechanical means because they are not chemically bound.

Explanation:

A pure substance is one that has a composition and characteristic properties that do not change, whatever the physical conditions in which it is found; that is, the physical transformations do not affect it. In other words, pure substances will be made up of particles that are identical to each other. Mechanical mixture are the result of the physical union of two or more substances which are called components, these can be elements or compounds, whose particles do not mix uniformly. The components of the mixtures have different properties, such as the state of aggregation, the density or the solubility. These properties allow substances to be identified and facilitate the separation of the components of a mixture, that is, through physical or mechanical processes we can isolate and obtain the components that make up the mechanical mixtures.

the answer is definitely a