Final answer:
Water in aerobic respiration is formed in the mitochondria during the electron transport chain, where oxygen combines with hydrogen ions to produce water.
Step-by-step explanation:
In aerobic respiration, water is formed at the end of the electron transport chain, which takes place inside the mitochondria of cells. Oxygen serves as the final electron acceptor and, after accepting electrons, it combines with hydrogen ions to form water (H₂O). This is part of a set of reactions that lead to the production of ATP, providing energy for cellular processes. The formation of water is a critical step in ensuring the continuous function of the electron transport chain, as it allows the chain to keep flowing by eliminating electrons and hydrogen ions, thereby creating a supply of ATP for the cell.