What characterizes a conjugate acid-base pair?

A conjugate acid-base pair is characterized by the relationship between an acid and its corresponding base, which differ by a single proton (H⁺ ion). When an acid donates a proton, it transforms into its conjugate base, and conversely, when a base accepts a proton, it becomes its conjugate acid. This relationship illustrates the fundamental concept of acid-base chemistry as defined by the Brønsted-Lowry theory.

For example, if we take acetic acid (CH₃COOH) as the acid, when it donates a proton, it becomes acetate (CH₃COO⁻), which is its conjugate base. Thus, the key distinction between the conjugate acid and its corresponding base is indeed the presence or absence of a proton, making option B the accurate characterization.