Asubstance that increases the concentration of hydroxide ions in aqueous solution.

The answer that complete the sentence is "Arrhenius base".

The complete sentence is: A substance that increases the concentration of hydroxide ions in aqueous solution is an Arrhenius base.

Arrhenius' acid and base model says that an acid is a substance that contains hydrogen and ionizes in aqueous solution producing protons (H+) and a base is a substance that cointains hydroxide and release it in aqueous solution.

D-no effect on the rate