MCAT General Chemistry Practice Exam 2026 – Comprehensive Test Prep

A Bronsted-Lowry base is defined as a proton acceptor. This theory, developed by Johannes Nicolaus Bronsted and Thomas Martin Lowry, focuses on the transfer of protons (H⁺ ions) in acid-base reactions. According to this definition, when a substance accepts a proton, it acts as a base within this framework.

In a typical acid-base reaction, the acid donates a proton to the base. For instance, if ammonia (NH₃) accepts a proton from water (H₂O), it forms NH₄⁺ (the ammonium ion), demonstrating that NH₃ acts as a Bronsted-Lowry base by accepting a proton.

Other options, like a proton donor, refer specifically to acids in this theory. Electron acceptors do not align with the Bronsted-Lowry definitions, as they pertain more to Lewis acids and bases rather than Bronsted-Lowry. Lastly, a substance that donates hydroxide ions describes characteristics of Arrhenius bases, which fall under a different acid-base theory. Thus, the correct concept of a Bronsted-Lowry base being a proton acceptor is clear within the definitions and reactions involved in acid-base chemistry.