They are completely dissociated . They are incompletely dissociated . Therefore, we can compare relative acid strengths by comparing K a values for acids. As K a increases, the acid strength increases, OR as pK a decreases, acid strength increases. Therefore, there is no undissociated nitric acid in water.
Some acids can donate more than one proton in aqueous solution.
It should make sense that it becomes progressively more difficult to remove successive protons, so we anticipate the corresponding acid dissociation constants to decrease.