What is a conjugate acid?

A conjugate acid is defined as the species that results when a base accepts a proton (H⁺ ion). In the context of acid-base chemistry, bases are substances that can accept protons, and when they do, they are transformed into their conjugate acids. This is a key concept in the Brønsted-Lowry theory of acids and bases, which emphasizes the transfer of protons during chemical reactions.

For example, when ammonia (NH₃), a basic substance, accepts a proton, it becomes ammonium (NH₄⁺), which is the conjugate acid of ammonia. This transformation illustrates the concept that bases become their conjugate acids when they gain protons.

In contrast, the other options describe different scenarios involving acids and bases but do not accurately define a conjugate acid. For instance, a particle formed when an acid accepts a proton refers to a different process leading to a conjugate base, while a base donating a proton relates to the formation of a conjugate base as well. The notion of a particle that cannot accept protons does not pertain to the definition of a conjugate acid. Understanding these definitions is essential for grasping the foundational concepts in acid-base chemistry.