Which statement best describes a polyprotic acid?

• A. An acid that donates two protons
• B. An acid that donates one proton
• C. An acid that donates multiple protons
• D. An acid that can donate more than one proton

Answer: (D)

The key idea is that polyprotic acids have more than one acidic hydrogen and can lose protons in multiple steps. The best way to describe them is that they can donate more than one proton, which covers acids like sulfuric acid (two protons) and phosphoric acid (three protons) that release protons successively. Saying they donate two protons is only true for diprotic acids and misses other polyprotic cases. Saying they donate multiple protons can be read as releasing several at once, which isn’t the usual stepwise behavior. Monoprotic acids, of course, donate only one proton.