In aqueous solution, Arrhenius acids increase the concentration of which ion?

• A. OH-
• B. H+
• C. Na+
• D. Cl-

Answer: (B)

Acids in water donate protons, which raises the concentration of hydrogen ions in solution. In aqueous solution, those protons are quickly solvated by water to form hydronium ions, so [H3O+] increases. That’s why the ion whose concentration goes up is hydrogen (as H+ or, effectively, H3O+). The other ions aren’t specifically produced by acid dissociation: OH- is associated with bases, and Na+ and Cl- are spectator ions that don’t reflect the defining action of an Arrhenius acid.