Final answer:
Strong acids and bases are 100% ionized in aqueous solution.
Step-by-step explanation:
Strong acids and bases are 100% ionized in aqueous solution, while weak acids and bases are less than 100% ionized. HCl, H2SO4, and HClO4 are all strong acids, so they are 100% ionized in aqueous solution. Therefore, the correct answer is option D) All of them.