Final answer:
Nitrogen-based pollutants are suspected to primarily affect the amphibian metamorphosis stage of their life cycle, particularly impacting the transitions tadpoles undergo to become adult frogs.
Step-by-step explanation:
The nitrogen-based pollutants are particularly suspicious in affecting the stage of amphibian metamorphosis. During metamorphosis, the amphibian's physiology changes dramatically, and any pollutants in the environment can have a significant impact on this vulnerable phase. The process of metamorphosis, as seen in the transition from a tadpole to a frog, involves significant developmental changes that are hormonally driven and could be disrupted by environmental contaminants. Since amphibians have permeable skin that readily absorbs substances from the environment, they are particularly sensitive to pollution, with the developmental stage of metamorphosis being one of the most critical periods for potential impacts.