Air is best described as ________.

• A. a heterogeneous mixture
• B. an element
• C. a compound
• D. a homogeneous mixture

Answer: (D)

Verified step by step guidance

1. Understand the definitions of the terms: an element is a pure substance consisting of only one type of atom; a compound is a pure substance made of two or more elements chemically combined in fixed proportions; a heterogeneous mixture has visibly different parts or phases; a homogeneous mixture has a uniform composition throughout.
2. Recognize that air is composed of several gases such as nitrogen, oxygen, carbon dioxide, and others mixed together physically but not chemically bonded.
3. Since the components of air are not chemically combined and the mixture is uniform throughout, air does not qualify as an element or a compound.
4. Because air's composition is consistent and uniform at the macroscopic level, it is classified as a homogeneous mixture rather than a heterogeneous mixture.
5. Therefore, the best description of air is a homogeneous mixture.