Which definition applies to a conjugate acid in Bronsted-Lowry acid-base theory?

In Bronsted-Lowry acid-base theory, a conjugate acid is defined as the species that forms when a Bronsted-Lowry base gains a proton (H⁺). The concept hinges on the idea that acids are proton donors and bases are proton acceptors. When a base accepts a proton, it transforms into its corresponding conjugate acid, thus creating a pair of acid-base relationships.

For example, if ammonia (NH₃) acts as a base by accepting a proton, it becomes ammonium (NH₄⁺), which is the conjugate acid of ammonia. This foundational aspect highlights that conjugate acids are inherently tied to their corresponding bases, making the identification of pairs central to understanding acid-base behavior.

The other definitions related to the other options don't accurately describe a conjugate acid in this theory. A conjugate acid is not defined solely by its interaction with bases, nor can it be categorized strictly as a weak acid, and it does play a significant role in determining the pH of a solution. Thus, "pairs with a Bronsted-Lowry base" best captures the relationship that defines a conjugate acid in this framework.