Two particles that differ from each other by only a proton (a hydrogen ion)

Bronsted-Lowry acid and base

Explanation:

The definition of Bronsted-Lowry for a compound is in its ability to deal with any solvent, such as ammonia or sulfuric acid, through acids and bases in pairs, called conjugated acid-base.

A Bronsted-Lowry base is any species capable of accepting a hydrogen proton, which requires a pair of free electrons to form the bond with the H⁺ proton, whereas a Bronsted-Lowry acid is a species capable of donating an H⁺.

Thus, the conjugated base of a Bronsted-Lowry acid is the species formed after that acid donates a proton. The conjugated acid of a Bronsted-Lowry base is the species formed after that base accepts a proton.

The two species in an acid-base conjugate pair have the same molecular formula, except that the acid has an extra H⁺ compared to the conjugated base.