Final answer:
The three groups of amphibians based on the environment in which they live as adults are terrestrial, arboreal, and aquatic. Terrestrial amphibians live on land, arboreal ones live in trees, and aquatic amphibians spend their lives in water.
Step-by-step explanation:
Amphibians are unique vertebrates known for their ability to thrive both in water and on land. The three main groups of amphibians based on their adult environment are: terrestrial, arboreal, and aquatic. Terrestrial amphibians are those that spend most of their adult life on land. Arboreal amphibians live in trees, exploiting the vertical aspect of the forest. Aquatic amphibians, on the other hand, spend much if not all of their adult lives in water.
Examples include frogs, which can be either terrestrial or arboreal, often living near bodies of water. Salamanders, another group of amphibians, include species that inhabit terrestrial or aquatic environments. Caecilians, though less known, are usually terrestrial or aquatic, with some species being burrowers, venturing underground.
Despite these groups, it's important to note that not all amphibians fit neatly into one category, as some may change habitats based on season, life cycle, or environmental conditions.