Final answer:
An Arrhenius base is a substance that dissociates to produce hydroxide ions in water. Mg(OH)2, or magnesium hydroxide, is an example of an Arrhenius base as it ionizes to produce Mg2+ and OH- ions in solution.
Step-by-step explanation:
An Arrhenius base is a substance that dissociates in water to yield hydroxide ions (OH-). A classic example of an Arrhenius base is Mg(OH)2, magnesium hydroxide. In an aqueous solution, an Arrhenius base like Mg(OH)2 will ionize, producing Mg2+ and OH- ions, thus increasing the OH- ion concentration in the solution.
The substances listed in the question such as HNO3, H2C2O4, HCIO4, H3PO4, H2SO4, and H2SO3 are examples of Arrhenius acids because they produce hydrogen ions (H+) when dissolved in water, not hydroxide ions (OH-).