Which of the following is true about amphoteric substances?

Amphoteric substances are defined by their unique ability to act as both acids and bases, which means they can either accept or donate protons (H⁺ ions) depending on the conditions of their environment. This characteristic aligns precisely with the correct answer choice.

When an amphoteric substance encounters a strong acid, it can accept a proton, thereby acting as a base. Conversely, when placed in a basic environment, it may donate a proton and thus behave as an acid. This dual capability makes them versatile in chemical reactions, particularly in titration processes and biochemical environments.

Understanding this concept is essential, as amphoteric behavior is crucial in various applications, including buffer systems in biological contexts and the operation of certain metal hydroxides in corrosion prevention. The other options provided do not accurately describe the properties of amphoteric substances, as they focus on unrelated characteristics such as corrosion behavior or solubility in water, which do not define amphotericity.