In the Brønsted-Lowry definition of acids and bases, an acid is a proton (H⁺) donor, and a base is a proton acceptor. When a Brønsted-Lowry acid loses a proton, a conjugate base is formed. Similarly, when a Brønsted-Lowry base gains a proton, a conjugate acid is formed. A Brønsted-Lowry acid (or base) and its conjugate base (or acid) are known as a conjugate acid-base pair.
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