* Element: A pure substance that cannot be broken down into simpler substances (e.g., zinc itself is an element).

* Compound: A substance formed by the chemical combination of two or more different elements in a fixed ratio (e.g., zinc oxide).

* Mixture: A combination of two or more substances where each substance retains its own properties. The components of a mixture can be separated by physical means.

Mossy zinc is formed when zinc metal reacts with the environment. This reaction involves the formation of zinc oxide (a compound), but it also includes other substances like dust, dirt, and maybe even some organic matter. Since the composition of mossy zinc can vary depending on the environment, it's considered a mixture.