Which theory defines acids as proton donors and bases as proton acceptors?

• A. Amphoteric species
• B. Bronsted-Lowry
• C. Amphiprotic species
• D. Polyprotic acid

Answer: (B)

Acids are proton donors and bases are proton acceptors is defined by the Brønsted–Lowry theory. In this view, an acid transfers a proton to a base; after the transfer, the acid becomes its conjugate base and the base becomes its conjugate acid. This framework explains many reactions in water and in other solvents by focusing on proton transfer rather than the state of the substance alone. For example, when a strong acid donates a proton to water, water acts as the base and becomes its conjugate acid (H3O+), while the acid becomes its conjugate base.

The other terms describe properties or capabilities of substances rather than the rule for acid–base interaction. Amphoteric or amphiprotic species can both donate and accept protons depending on the partner, but that’s about behavior, not the defining theory. Polyprotic acids just indicate the ability to donate more than one proton, not the acid–base interaction framework itself.