Answer: The correct statement is a hydronium ion donor in a reaction.

Explanation:

According to Arrhenius concept, a base is defined as a substance which donates hydroxide ions (OH^-) when dissolved in water and an acid is defined as a substance which donates hydronium ions (H_3O^+) in water.

According to the Bronsted Lowry conjugate acid-base theory, an acid is defined as a substance which donates protons and a base is defined as a substance which accepts protons.

According to the Lewis concept, an acid is defined as a substance that accepts electron pairs and base is defined as a substance which donates electron pairs.

A substance that increases the hydroxide ion concentration of a solution is an Arrhenius base.

Hence, the correct statement is a hydronium ion donor in a reaction.