Acids are substances that release hydrogen ions since they have hydrogen in their formula. You should also know that the hydrogen ions are protons from the acid and are attracted to the negatively charged oxygens in a water molecule. Moreover, bases are substances that release hydroxide ions since they have hydroxide in their formula. SO does this mean the opposite of ionization (also known as dissociation to release hydroxide) are bases for certain? Not really. For Arrhenius acid base definition then yes. However, under the Bronsted-Lowry acid base definition, it is more about the acceptance of a proton! Similarly for acids, it is about the donation of a proton.