Final answer:
Uric acid is the water-insoluble compound like purines that forms a white paste or powder, and it is excreted by birds, reptiles, and insects.
Step-by-step explanation:
The water-insoluble compound that is similar to purines found in nucleic acids and tends to form a white paste or powder is uric acid. Uric acid is a byproduct of nucleic acid metabolism, and it is excreted primarily by birds, insects, and reptiles as a way of getting rid of toxic nitrogen compounds. In comparison to other substances, such as urea and ammonia, uric acid is much less soluble in water. The conversion of ammonia to uric acid is an energy-intensive process, which makes it less favorable for many animals, but necessary for those that need to conserve water, such as birds and reptiles.