Answer
A 2.0 L solution of 3.0 M HCl solution will consist of 6 moles of $H^+$ and $Cl^-$.
A 2.0 L solution of 3.0 M $HC_2H_3O_2$ will have few $H^+$ and $C_2H_3O_2^-$ ions and remain mostly intact.
Work Step by Step
Strong acids completely dissociate in solution. Therefore, because HCl is a strong acid and we have $2.0 * 3.0 =6.0$ moles of HCl, we will have 6 moles of $H^+$ and $Cl^-$.
Weak acids only partially dissociate in solution. Therefore, because $HC_2H_3O_2$ is a weak acid, it will remain mostly intact with few ions in solution.
