Air is made up of different gases, such as oxygen, nitrogen, and carbon dioxide. Which statement best describes these three components of air?

A pure substance has a fixed composition and consists of one kind of particle. Oxygen and nitrogen are elements, while carbon dioxide is a compound; each is a pure substance when considered separately. In air, they are mixed together rather than chemically bonded to one another, so the best choice is that all three are classified as pure substances.

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