What is always true of a weak acid ?

Answer: D. it only partially dissociates in solution.
Explanation:
Strong acid is defined as the acid which completely dissociates when dissolved in water. They have low pH. These releases [tex]H^+[/tex] ions in their aqueous states.
[tex]HNO_3(aq.)\rightarrow H^+(aq.)+NO_3^-(aq.)[/tex]
Weak acid is defined as the acid which does not completely dissociates when dissolved in water. They have high pH. These releases [tex]H^+[/tex] ions in their aqueous states.
[tex]CH_3COOH\rightleftharpoons CH_3COO^-+H^+[/tex]
Thus the correct option is it only partially dissociates in solution.