When an arrhenius base is dissolved in h2o, the only negative ion present in the solution is?

Answer is: hydroxide ions (OH⁻).

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) or barium hydroxide: Ba (OH) ₂ (aq) → Ba²⁺ (aq) + 2OH⁻ (aq).

According to this theory acids are substances which produce hydrogen ions in water solution.