Final answer:
In a 0.10 M solution of a strong acid (HA), the concentration of hydronium ions ([H3O+]) is 0.10 M.
Step-by-step explanation:
In a 0.10 M solution of a strong acid (HA), the acid is fully ionized, meaning that it completely dissociates into its ions. Therefore, the concentration of hydronium ions ([H3O+]) in the solution is 0.10 M. Since the acid is strong, its conjugate base concentration ([A-]) is negligible.