Here's why:

* Elements are pure substances that cannot be broken down into simpler substances by chemical means (e.g., gold, oxygen).

* Compounds are formed when two or more elements chemically combine in a fixed ratio (e.g., water, salt).

* Mixtures are combinations of two or more substances where each substance retains its own chemical identity. They are not chemically bonded and can be separated by physical means (e.g., sand and water, air).

There are two main types of mixtures:

* Homogeneous mixtures have a uniform composition throughout (e.g., saltwater).

* Heterogeneous mixtures have a non-uniform composition (e.g., sand and gravel).

So, mixtures are the large class of matter that encompasses both elements and compounds.