Final answer:
Inhaled aerosol drugs that absorb moisture are considered hygroscopic. Such substances are hydrophilic and can attract water molecules, unlike hydrophobic substances which repel water.
Step-by-step explanation:
Inhaled aerosol drugs that are heterodisperse in size and absorb moisture readily are described as hygroscopic. This term refers to a substance's ability to attract and hold water molecules from the surrounding environment.
Hygroscopic materials are typically hydrophilic, which means they are "water-loving" and tend to mix with, dissolve, or be wetted by water. In contrast, hydrophobic substances repel water and do not mix well with it.
Molecules that contain both polar (water-attracting) and nonpolar (water-repelling) groups are known as amphipathic. These materials have regions that are hydrophilic and others that are hydrophobic,
such as fatty acid groups which are hydrophobic, whereas phosphate groups are hydrophilic in nature.
Inhaled aerosol drugs that readily absorb moisture and are heterodisperse in size are considered hydroscopic.
Hydroscopic substances have a strong attraction to water molecules and readily absorb moisture from the surrounding environment. This can affect the performance and stability of the aerosol drugs.