Answer is: B. Hydroxide ions.
An Arrhenius base is a substance that dissociates in water to form hydroxide ions (OH⁻).
For example sodium hydroxide: NaOH(aq) → Na⁺(aq) + OH⁻(aq).
Another example, balanced chemical reaction: Ba(OH)₂(aq) → Ba²⁺(aq) + 2OH⁻(aq).
According to the Arrhenius definition barium hydroxide is base.
Acids and bases when react (neutralisation) produce salt and water.
the answer is 75.0%.