According to the Bronsted-Lowry definition, which statement is correct?

• A. An acid donates an electron pair; a base accepts an electron pair.
• B. An acid donates a proton; a base accepts a proton.
• C. An acid donates a proton; a base donates a proton.
• D. An acid accepts a proton; a base donates a proton.

Answer: (B)

Bronsted-Lowry theory focuses on proton transfer. An acid is a substance that donates a proton (H+), and a base is one that accepts a proton. This simple idea explains how many acid–base reactions proceed: the acid gives away H+, and the base takes it. After donation, the original acid becomes the conjugate base, and after acceptance, the base becomes the conjugate acid. For example, HCl donates a proton to water, forming H3O+ and Cl−, while ammonia accepts a proton to become NH4+. The correct statement captures this proton-transfer relationship: acids donate protons and bases accept protons. Other descriptions either mix in electron-pair transfer (that’s a Lewis acid–base concept) or reverse the roles or imply both donate protons, which doesn’t align with the proton-transfer idea.