Which of the following is an example of a homogeneous mixture?

A homogeneous mixture is one in which the components are uniformly distributed and the composition is consistent throughout the mixture. In the context of the choices, air is the best example of a homogeneous mixture.

Air is composed of various gases, primarily nitrogen and oxygen, along with small amounts of other gases such as carbon dioxide and argon. Despite containing multiple substances, the gases are mixed together to such an extent that any sample of air taken from a location will have a similar composition and properties, demonstrating uniformity.

In contrast, soil is a heterogeneous mixture because it contains visible particles of organic matter, minerals, and various other components that can be identified separately. Chocolate chip cookies are also a heterogeneous mixture, as you can distinguish the chocolate chips from the cookie dough. Similarly, a mixture of sand and water is not uniform; the sand particles will settle at the bottom, creating separate phases that can be distinguished.