When water undergoes auto-ionization, which of the following species are produced?

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

Answer: (C)

Verified step by step guidance

1. Understand the concept of auto-ionization of water: it is a process where two water molecules react with each other to produce ions.
2. Write the chemical equation for the auto-ionization of water: \$2 \mathrm{H_2O} (l) \rightleftharpoons \mathrm{H_3O^+} (aq) + \mathrm{OH^-} (aq)$.
3. Recognize that the species produced are the hydronium ion (\(\mathrm{H_3O^+}\)) and the hydroxide ion (\(\mathrm{OH^-}\)), not free protons (\(\mathrm{H^+}\)) or other ions like \(\mathrm{Cl^-}\) or \(\mathrm{O^{2-}}\).
4. Note that \(\mathrm{H^+}\) ions in water are better represented as \(\mathrm{H_3O^+}\) because protons associate with water molecules immediately.
5. Conclude that the correct species produced by auto-ionization of water are \(\mathrm{H_3O^+}\) and \(\mathrm{OH^-}\).