Final answer:
Water is an example of an amphoteric substance that can act as both an acid and a base depending on the reaction. This behavior is called amphiprotism.
Step-by-step explanation:
Water is an example of an amphoteric substance, meaning it can act as both an acid and a base. In certain reactions, water can donate a hydrogen ion and act as an acid, while in other reactions it can accept a hydrogen ion and act as a base. This ability to behave as an acid or a base is called amphiprotism. For example, water can act as an acid when reacting with a stronger base like NH3 or as a base when reacting with a stronger acid like HF.