Here's why:

* Homogeneous mixture: A mixture where the components are evenly distributed throughout. Examples include saltwater, air, or sugar dissolved in water.

* Pure substance: A substance composed of only one type of molecule. Examples include water (H₂O), oxygen (O₂), and gold (Au).

Distilled water is produced by boiling water and collecting the steam, which is then condensed back into water. This process removes impurities like minerals and salts, leaving behind essentially pure water.

Since distilled water contains only water molecules (H₂O), it meets the definition of a pure substance.