Which of the following substances can be considered a mixture?

Saltwater is classified as a mixture because it consists of two or more substances that retain their individual properties. In saltwater, salt (sodium chloride) is dissolved in water, creating a solution where both components can be separated by physical means, such as evaporation. This characteristic of mixtures allows the different substances within them to maintain their individual chemical identities and properties.

In contrast, carbon dioxide, gold, and distilled water are not mixtures. Carbon dioxide is a compound formed by the chemical combination of carbon and oxygen in a fixed ratio. Gold is a pure element and does not consist of multiple components; it is a single type of atom. Distilled water is also a pure substance as it consists solely of H2O molecules, with no additional components present. Therefore, the nature of saltwater as a solution formed from distinct substances that can be separated highlights why it is classified as a mixture.