Which term describes a substance that can act as both an acid and a base, depending on the reaction context?

• A. Amphiprotic species
• B. Amphoteric species
• C. Bronsted-Lowry
• D. Buffer Solution

Answer: (B)

The concept tested is the dual behavior of certain substances in acid–base chemistry. An amphoteric substance can act as an acid in some reactions and as a base in others, depending on what it encounters.

This is why the term amphoteric fits best: it describes a species that can donate a proton in one context and accept a proton in another, showing both acidic and basic behavior. A classic example is water, which can donate a proton to a base to form OH−, or accept a proton to form H3O+. Metal oxides and hydroxides, like ZnO or Al2O3, also dissolve or react differently with acids and bases, illustrating the same idea.

Bronsted–Lowry refers to the general definitions of acid and base, not to a substance’s ability to behave as both in different contexts. A buffer solution is about resisting pH change, not about dual acid–base identity. Amphiprotic is related—it's a more specific term about proton transfer—but the broad, encompassing description of reacting as both acid and base in varying contexts is captured by amphoteric.