____ are formed when liquids evaporate into the air.

Vapors are formed when liquids evaporate into the air. This process occurs when molecules at the surface of a liquid gain enough energy to break free and transition into a gaseous state. This transformation is a fundamental principle of physical chemistry and is commonly observed with various liquids, such as water, alcohol, and solvents.

In the case of vapors, they typically exist in a state that is closer to the liquid form, with the capability to condense back into a liquid if cooled. This characteristic distinguishes vapors from gases, which are often comprised of substances that are fully in the gaseous state and do not readily revert to liquid under normal conditions.

The other terms, while related to the properties of matter and air, refer to different phenomena. Fumes are generally associated with smoke or fine particles produced by combustion. Aerosols consist of tiny solid or liquid particles suspended in a gas but include more complex mixtures than vapors. Gases, in contrast, are forms of matter that have no fixed volume or shape and can be comprised of various chemical substances.

Thus, the definition and physical behavior of vapors align directly with the process of evaporation from liquids, making it the correct answer in this context.