Question

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

Answer 1

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.