There is no acid dissociation constant for the element hydrogen (H). The acid dissociation constant, also known as the acidity constant or Ka, is a measure of the strength of an acid in solution. It is defined as the equilibrium constant for the dissociation of an acid into its conjugate base and a hydrogen ion (H⁺). Since hydrogen is not an acid, it does not dissociate and therefore does not have an acid dissociation constant.