A strong acid is one which reacts
completely with water to produce
hydronium ions. In other words, a strong
acid is fully deprotonated in water.
If each molecule of strong acid in the animation represents one mole of HX, then in aqueous solution, we have six moles of hydronium ions and six moles of X- ions, and no moles of HX molecules.
The common strong acids are HCl, HBr, HI, HNO3, HClO4, HClO3, and H2SO4 (to HSO4-).