Here's why:

* Mixture: A mixture is a combination of two or more substances that are not chemically bonded. The substances in a mixture retain their individual properties.

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

Salt is formed by the chemical reaction of sodium (Na) and chlorine (Cl). The resulting compound, NaCl, has properties completely different from either sodium or chlorine.