Define Bronsted-Lowry acid and base and provide an example of a conjugate acid-base pair.

• A. Acid donates a proton; base accepts a proton; example: HCl and Cl-.
• B. Acid accepts a proton; base donates a proton; example: NH3 and NH4+.
• C. Bronsted-Lowry theory defines electron transfer.
• D. A conjugate acid-base pair is formed only when water is the solvent.

Answer: (A)

The key idea is proton transfer: an acid donates a proton and a base accepts a proton. In the example, hydrochloric acid donates a proton to water, producing chloride ion and hydronium ion. This shows HCl as the acid and Cl− as its conjugate base, while water becomes H3O+ and is the conjugate acid of the base water. A conjugate acid-base pair is simply two species that differ by one proton, such as HCl and Cl−. The other statements don’t fit because they mix up who donates or accepts a proton, rely on electron transfer, or claim conjugate pairs only form in water.