Final answer:
Strong acids and bases completely ionize in water, such as hydrogen chloride and barium hydroxide, whereas weak acids and bases only partially ionize.
Step-by-step explanation:
The types of acids and bases that completely ionize in water are strong acids and strong bases. When these substances dissolve in water, they dissociate fully into their ions. Strong acids, such as hydrogen chloride (HCl), ionize completely into hydrogen ions (H+) and the corresponding anions (Cl-).
Similarly, strong bases like barium hydroxide (Ba(OH)2) dissociate into hydroxide ions (OH-) and the corresponding cations (Ba2+). In contrast, weak acids and weak bases only partially ionize in water, resulting in an equilibrium between the ionized and non-ionized forms of the acid or base.