Which statement best describes a monoprotic acid?

• A. An acid that donates more than one proton
• B. An acid that donates only one proton
• C. An acid that donates protons and electrons
• D. An acid that ionizes completely

Answer: (B)

Monoprotic acids are defined by donating a single hydrogen ion per molecule when dissolved. That means the defining feature is one proton released in solution, regardless of how completely the acid ionizes. For example, hydrochloric acid and acetic acid both donate exactly one proton per molecule, even though one is a strong acid and the other is weak. The other statements miss this key idea: donating more than one proton describes polyprotic acids; donating protons and electrons mixes in redox concepts that aren’t part of how we define acids here; and ionizing completely is about acid strength, not the number of protons an acid can donate. So the statement that the acid donates only one proton best matches the concept of monoprotic acids.