Which of the following is NOT a form of matter?

The answer identifies that plasma and air combined is not considered a distinct form of matter. Matter typically exists in four primary states: solids, liquids, gases, and plasma. Each of these states has specific characteristics based on factors such as temperature and pressure, which dictate how the particles are arranged and behave.

Plasma is often referred to as the fourth state of matter, distinct from solids, liquids, and gases due to its ionized particles that conduct electricity and respond to magnetic fields. Air, on the other hand, is a mixture of gases, primarily nitrogen and oxygen, and does not represent a separate state of matter. Combining plasma and air does not create a new or different state; rather, it merely refers to a mixture containing plasma and gaseous air components.

Understanding the nature of how these forms of matter interact and exist will help clarify why the other options—solids, liquids, and gases—are fundamental states of matter recognized in both scientific study and practical applications in fields like chemistry and physics.