Answer : The structure of atom shows unity in forming a particular molecule, different atoms of different or same elements combine to form a molecule. This shows the unity in formation of molecules from atoms. Like H and O atom combines to give water molecule.
Diversity is from the union of atoms which defines their states of matter. As in solids,liquid and gaseous forms; the atoms combine to form a molecule which may or may not belong from the same state of the elements. Like H is in gaseous form and O is also in gaseous form, but water is in liquid state.
So, it is clear that the structure of atoms helps in ifentifying both unity and diversity in forms of matter.