Strong acids are acids that completely dissociate or ionize in water, releasing all of their hydrogen ions (H+). In other words, they undergo complete ionization in water. As a result, they have a high concentration of H+ ions and a low pH.

Some common examples of strong acids include:

- Hydrochloric acid (HCl): HCl completely dissociates in water, releasing H+ and Cl- ions.

- Sulfuric acid (H2SO4): H2SO4 ionizes in two steps. In the first step, it releases two H+ ions and HSO4- ions. In the second step, the HSO4- ion further dissociates to release another H+ ion and SO42- ions.

- Nitric acid (HNO3): HNO3 completely dissociates in water, releasing H+ and NO3- ions.

- Hydroiodic acid (HI): HI completely dissociates in water, releasing H+ and I- ions.

- Perchloric acid (HClO4): HClO4 completely dissociates in water, releasing H+ and ClO4- ions.

These acids are considered strong because they completely ionize in water, regardless of their concentration. This means that even at low concentrations, they will still release all of their H+ ions and have a low pH.

In contrast, weak acids only partially dissociate in water, meaning that they do not release all of their H+ ions. This results in a lower concentration of H+ ions and a higher pH compared to strong acids.