What is air classified as within the realm of physics?

Air is classified as a fluid in the realm of physics because it possesses the ability to flow and take the shape of its container. This classification stems from the characteristics of fluids, which include both liquids and gases. Although air is specifically a gas, it is also categorized within the broader definition of fluids.

Fluids are substances that can deform continuously under an applied shear stress, which is evident in how air moves and interacts with objects in its path. The molecular structure of air allows for compressibility and expansion, differentiating it from solids and liquids, which have fixed shapes and volumes. Therefore, identifying air as a fluid encompasses its behavior and properties in physics, making this the most accurate classification from the available options.