What term describes a substance that can act as either an acid or a base?

A substance that can act as either an acid or a base is described as amphoteric. This means it has the ability to both donate protons (acting as an acid) and accept protons (acting as a base) depending on the conditions of the chemical reaction it is involved in.

Amphoteric substances, like water or amino acids, can participate in reactions where they can either interact with stronger acids or stronger bases. This dual functionality is important in various chemical processes, including biological systems where maintaining pH balance is crucial.

Other terms in the choices represent different concepts. An electrolyte refers to a substance that dissociates into ions in solution, which is essential for conducting electricity in solutions. An oxidizing agent in a redox reaction gains electrons and is reduced, while a buffer is a solution that resists changes in pH upon the addition of small amounts of acid or base but is not defined by its ability to act as both an acid and a base. Therefore, the term that accurately describes a substance capable of acting as both an acid and a base is amphoteric.