Final answer:
A mixture can be made up of two or more pure substances mixed together, including elements and compounds. The composition of a mixture can be either homogeneous or heterogeneous.
Step-by-step explanation:
A mixture can be made up of two or more pure substances mixed together. These pure substances can be elements, compounds, or a combination of both. Mixtures can be classified as homogeneous or heterogeneous, depending on whether their composition is uniform throughout or not.