Which theory defines acids as substances that produce hydronium in water and bases as substances that produce hydroxide in water?

• A. Bronsted-Lowry
• B. Arrhenius
• C. Lewis
• D. Conjugate acid-base

Answer: (B)

In water, acids are defined by Arrhenius as substances that, when dissolved, increase the concentration of hydronium ions (H3O+), because they release H+ that quickly attaches to water molecules. Bases, in this view, dissociate to produce hydroxide ions (OH-), increasing the OH- concentration in the solution. This solvent-based perspective cleanly explains why common acids like HCl yield acidic aqueous solutions (H3O+ formed from H+ in water) and bases like NaOH produce basic solutions (OH- in solution). Other definitions broaden the scope: Brønsted-Lowry focuses on proton donation and acceptance regardless of solvent, Lewis centers on electron-pair transfer, and the idea of conjugate acid-base pairs describes relationships between species that differ by a proton rather than a solvent-specific rule.