According to the principles of chemical bonding and molecular geometry found in the sources, the properties of the two species are determined as follows:

1. $NO_{3}^{-}$ (Nitrate ion): The central nitrogen atom has five valence electrons, and the ion carries a negative charge. It is isoelectronic with the carbonate ion ($CO_{3}^{2-}$) . The nitrogen atom undergoes $sp^{2}$ hybridisation and adopts a trigonal planar structure to accommodate three bonding domains with no lone pairs on the central atom .
2. $H_{3}O^{+}$ (Hydronium ion): The central oxygen atom has six valence electrons, one of which is lost to form the cation. It forms three bonds with hydrogen atoms and retains one lone pair. As stated in the sources, this results in $sp^{3}$ hybridisation and a trigonal pyramidal geometry .

Because $NO_{3}^{-}$ is $sp^{2}$ (planar) and $H_{3}O^{+}$ is $sp^{3}$ (pyramidal), the two species have dissimilar hybridisation for the central atom and different structures.