Which of the following substances is a byproduct of carbon dioxide in water?

Bicarbonate is the correct answer because when carbon dioxide (CO2) dissolves in water, it interacts with water molecules to form carbonic acid (H2CO3). This reaction is a key process in both natural water systems and in biological contexts. The carbonic acid can then dissociate into bicarbonate (HCO3-) and hydrogen ions (H+).

This conversion is essential for maintaining pH balance in aquatic environments and plays a critical role in the carbon cycle. The presence of bicarbonate serves as an important buffer, helping to stabilize pH levels in water bodies, which is crucial for the health of aquatic organisms.

The other substances mentioned—hydrogen sulfide, ammonia, and phosphate—are not directly formed as byproducts of carbon dioxide in water and relate to different biochemical processes or nutrient cycles within aquatic ecosystems.