Here's a breakdown:

* Arrhenius Definition: An Arrhenius base is a substance that produces hydroxide ions (OH-) when dissolved in water.

* Brønsted-Lowry Definition: A Brønsted-Lowry base is a substance that accepts a proton (H+). When a base accepts a proton from water, it forms a hydroxide ion (OH-).

Example:

Sodium hydroxide (NaOH) is a strong base. When dissolved in water, it dissociates into sodium ions (Na+) and hydroxide ions (OH-):

NaOH(aq) → Na+(aq) + OH-(aq)

This is why solutions of bases have a pH greater than 7. The hydroxide ions contribute to the alkalinity of the solution.