How do weak acids behave in a solution?

Weak acids behave in a solution by not fully ionising, meaning that only a small proportion of the acid molecules dissociate into ions. This partial ionisation is a characteristic feature of weak acids, resulting in an equilibrium between the undissociated acid and the ions in the solution.

For example, in the case of acetic acid (a common weak acid), when it is dissolved in water, only a fraction of the acetic acid molecules give up their hydrogen ions (H⁺) to form acetate ions (CH₃COO⁻). This leads to a situation where both the dissociated ions and the undissociated molecules coexist in the solution, resulting in a relatively low concentration of hydrogen ions and a higher pH compared to strong acids, which fully dissociate.

This behavior is contrasted with strong acids, which fully dissociate into their respective ions in solution, leading to a very high concentration of hydrogen ions. Thus, the defining aspect of weak acids is their incomplete ionisation in aqueous solutions, confirming why the chosen answer is accurate.