Nitric acid (HNO3) is a stronger acid than phosphoric acid (H3PO4) because it is able to completely dissociate in water, releasing H+ and NO3- ions. Phosphoric acid, on the other hand, only partially dissociates, releasing H+ and H2PO4- ions. The strength of an acid is determined by its ability to release H+ ions.

The pH of a solution is a measure of its acidity or basicity. The lower the pH, the more acidic the solution. Nitric acid has a lower pH than phosphoric acid, indicating that it is a stronger acid.

The strength of an acid also affects its corrosive properties. Nitric acid is more corrosive than phosphoric acid because it is able to dissolve metals and other materials more quickly.

In summary, nitric acid is more powerful than phosphoric acid because it is more acidic, has a lower pH, and is more corrosive.