Final answer:
For a monoprotic strong acid, the acid concentration is equal to the concentration of hydronium ions, since the acid fully dissociates in solution.
Step-by-step explanation:
For a monoprotic strong acid, the acid concentration is equal to the concentration of the hydronium ions [H3O+]. This is because strong acids completely dissociate in water. For instance, if you have a monoprotic strong acid like HCl or HNO3, and the solution is 0.50 M, then the concentration of hydronium ions will also be 0.50 M. This differs from weak acids where the acid does not completely dissociate and the concentration of hydronium ions will be much less than the molar concentration of the acid.