Final answer:
Acids release hydrogen ions (H+) in solution. Strong acids completely release all of their hydrogen ions, while weak acids do not ionize completely.
Step-by-step explanation:
An acid is a substance that releases hydrogen ions (H+) in solution. Hydrogen ions are released because an atom of hydrogen has just one proton and one electron, and a positively charged hydrogen ion is simply a proton. Strong acids completely release all of their hydrogen ions in solution, while weak acids do not ionize completely and some of the hydrogen ions remain bonded within a compound. For example, hydrochloric acid (HCl) is a strong acid that aids in digestion and kills ingested microbes.