What varieties of matter may be the constituents in mixtures?

Answer: two or more different pure substances, which may be elements or compounds.

Explanation:

The term varieties of matter is kind of ambiguos since it is not defined.

The best approach to the question is to think of matter as it can be classified into to kinds: pure substaces and mixtures.

Elements and compounds are pure substances.

Elements are pure substances constituted by only one kind of atoms. An element cannot be divided into simpler substances either by physical or chemical media.

A compound is a chemical combination of two or more different elements. A compound can be divided into simpler substances by chemical reactions, but not by physical media. The properties of compounds are different of those of the elements of which they are constituted. The composition of a compoind (ratio among its elements) is fixed.

A mixture is the physical combination of two or more pure substances (either different elements or compounds) which can be mixed in any proportion. This is, its composition is variable. The substances that form the mixture can be separated by physical media.