In the given definitions, what role does an acid play?

• A. Proton donor
• B. Proton acceptor
• C. Electron donor
• D. Oxidizing agent

Answer: (A)

In acid-base chemistry, the defining action of an acid is to donate a proton. When acids meet bases, the acid gives away a hydrogen ion (a proton) to the base, forming its conjugate base. This proton transfer explains why acids lower pH and drive the formation of conjugate pairs. The other roles don’t fit as the primary action of an acid: a proton acceptor is a base, an electron donor relates to reducing agents or Lewis bases in different contexts, and an oxidizing agent is about accepting electrons in redox reactions rather than transferring protons. So the proton-donating role is the correct description.