Which of the following is a prominent example of an amphoteric substance?

Water is a prime example of an amphoteric substance because it can act as both an acid and a base depending on the context of the reaction. In acidic conditions, water can donate a proton (H+) to form hydroxide ions (OH-), thus displaying its behavior as a Brønsted-Lowry base. Conversely, in basic conditions, water can accept a proton to form hydronium ions (H3O+), behaving as a Brønsted-Lowry acid. This dual capability allows water to participate in various chemical reactions, making it a versatile molecule in both acid-base chemistry and in biological systems.

In contrast, the other choices do not exhibit this dual behavior. Hydrochloric acid is primarily an acid and does not act as a base. Sodium chloride is a neutral salt that does not participate in acid-base reactions. Ammonia, while it behaves as a base by accepting protons, does not exhibit the acidic behavior characteristic of amphoteric substances. Thus, water stands out as the quintessential example of an amphoteric substance.