Which statement best defines an Arrhenius acid?

• A. A substance that donates an electron pair to form a coordinate covalent bond
• B. A substance that increases the concentration of $O^{2^{-}}$ in the gas phase
• C. A substance that increases the concentration of $H^{+}$ in aqueous solution
• D. A substance that increases the concentration of $O^{2^{-}}$ in aqueous solution

Answer: (C)

Verified step by step guidance

1. Recall the Arrhenius definition of acids and bases: An Arrhenius acid is a substance that increases the concentration of hydrogen ions (H\textsuperscript{+}) in aqueous solution.
2. Identify that the key characteristic of an Arrhenius acid is its ability to release or produce H\textsuperscript{+} ions when dissolved in water.
3. Understand that other options, such as donating an electron pair or increasing the concentration of superoxide ions (O\textsubscript{2}\textsuperscript{−}), do not fit the Arrhenius acid definition.
4. Recognize that the correct statement must specifically mention increasing H\textsuperscript{+} concentration in aqueous solution to align with the Arrhenius acid concept.
5. Conclude that the best definition of an Arrhenius acid is: 'A substance that increases the concentration of H\textsuperscript{+} in aqueous solution.'