* Substance: A substance is a pure form of matter with a consistent composition and properties. Examples include gold, oxygen, and water.

* Mixture: A mixture is a combination of two or more substances that are not chemically bonded. The components of a mixture retain their individual properties. Examples include sand and water, or air.

* Compound: A compound is formed when two or more different elements chemically combine in a fixed ratio. The resulting compound has properties distinct from the original elements.

Table salt is a compound because it is formed from the chemical combination of sodium (Na) and chlorine (Cl) in a 1:1 ratio (NaCl). This chemical bond creates a new substance with properties entirely different from either sodium or chlorine.