Final answer:
In the Brønsted-Lowry theory, acids are defined as substances that donate a proton (H+), and bases are those that accept a proton; thus, the answer is c. H+.
Step-by-step explanation:
Brønsted-Lowry Acids and Bases
According to the Brønsted-Lowry theory, both acids and bases are defined based on their ability to lose or gain protons. An acid is a substance that can donate a proton (H+), and a base is a substance that can accept a proton. This theory extends the definitions beyond just aqueous solutions, allowing for a broader range of acid-base reactions.
In the context of Brønsted-Lowry theory, the correct answer to the students' question on what substances lose or gain in acid-base reactions would be c. H+. This differs from the Arrhenius definition, which restricts acids and bases to aqueous solutions and defines acids as producers of H+ ions and bases as producers of OH- ions.