Question

What are `"pure substances?"`

Answer 1

A pure substance has a definite composition, i.e. a specific formula that gives rise to specific ratios, and definite physical properties, i.e. melting point, boiling point etc.

Explanation:

`NaCl` has percentage by mass, `Na` `39.3%,` `Cl` `61.7%`; it doesn't matter if a milligram, a gram, or a kilogram sample of salt is analyzed. The proportions are going to be the same.