Here's why:

* Matter: Anything that takes up space and has mass.

* Pure Substance: A material with a fixed and definite composition. It cannot be separated into simpler substances by physical means.

Examples of pure substances include:

* Elements: Substances that cannot be broken down into simpler substances (e.g., gold, oxygen, carbon).

* Compounds: Substances formed by the chemical combination of two or more elements in a fixed ratio (e.g., water, salt, sugar).