Final answer:
HNO₂ is a weak acid because it partially dissociates in water, unlike strong acids that fully dissociate. The equilibrium between undissociated acid and ions is a key characteristic of weak acids.
Step-by-step explanation:
HNO₂, also known as nitrous acid, is a weak acid. It does not completely dissociate in water, which is a characteristic behavior of weak acids. Strong acids, such as HCl or H₂SO₄, dissociate almost completely in water. For weak acids like HNO₂, they partially dissociate, establishing an equilibrium between the undissociated acid and the ions in solution. This can be represented by the equilibrium chemical equation for the partial ionization of HNO₂, which shows that both ions and the undissociated form coexist in the solution.
In contrast, strong bases such as NaOH fully dissociate in water, and weak bases like NH₃ show only partial dissociation. Understanding the difference between strong and weak acids and bases is crucial when predicting the behavior of substances in various chemical reactions.