Which of the following substances is a mixture?

Granulated sugar and seawater are mixtures while sodium chloride and iron filings are pure substances. A mixture is a combination of two or more substances in which each substance retains its own chemical properties and can be separated from the mixture by physical means. Granulated sugar is a mixture of two or more types of sugar crystals. Seawater is a mixture of water, salt, and other minerals. A pure substance, on the other hand, has a fixed chemical composition and distinct chemical and physical properties. Sodium chloride is a pure substance because it is made up of only sodium and chloride ions and has a fixed chemical composition. Iron filings are also a pure substance because they are made up of only iron atoms and have a fixed chemical composition.