The correct option is A Ammonia
The tadpole of the frog is ammonotelic meaning it excretes their nitrogenous wastes in the form of ammonia. Ammonia is highly soluble in water with which it forms ammonium hydroxide. Ammonia is the first metabolic waste product of protein metabolism. Generally, the amphibians, the larval tadpoles excrete ammonia, while the adults produce urea.
So, the correct answer is option D.