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

A homogeneous mixture is one in which the components that make up the mixture are uniformly distributed and cannot be distinguished from one another, even under a microscope. In this case, the air we breathe is a prime example of a homogeneous mixture because it is composed of a variety of gases, such as nitrogen, oxygen, carbon dioxide, and others, that are evenly mixed together. These gases do not separate and remain consistent throughout, making it impossible to identify different components without specialized equipment.

In contrast, a chocolate chip cookie contains distinct components, such as chocolate chips and dough, which can be physically separated and are not uniformly distributed. A piece of aluminum foil is a pure substance, not a mixture, as it is made entirely of the element aluminum. Similarly, a piece of wood consists of various organic compounds and fibers, displaying varying structures and compositions, making it heterogeneous. Therefore, the air is the only option that exemplifies a homogeneous mixture.