Pure water can ionize into which of the following?

• A. H+ and Cl-
• B. H3O+ and OH-
• C. H2 and O2
• D. H+ and O2-

Answer: (B)

Verified step by step guidance

1. Understand that pure water undergoes a process called autoionization or self-ionization, where water molecules react with each other to form ions.
2. Recall the chemical equation for the autoionization of water: \$2\,\mathrm{H_2O} \rightleftharpoons \mathrm{H_3O^+} + \mathrm{OH^-}\(, where one water molecule donates a proton to another, producing hydronium (\)\mathrm{H_3O^+}\() and hydroxide (\)\mathrm{OH^-}$) ions.
3. Recognize that ions like \(\mathrm{H^+}\) and \(\mathrm{Cl^-}\) or \(\mathrm{H^+}\) and \(\mathrm{O^{2-}}\) do not result from pure water ionization because chloride and oxide ions are not present in pure water.
4. Note that \(\mathrm{H_2}\) and \(\mathrm{O_2}\) are gases produced by water electrolysis, not by its ionization.
5. Conclude that the correct ion pair formed by pure water ionization is \(\mathrm{H_3O^+}\) and \(\mathrm{OH^-}\).