Here's why:

* Molecular solids are formed by the attraction between molecules. These attractions are relatively weak, such as Van der Waals forces.

* Nitrogen exists as diatomic molecules (N₂) held together by strong covalent bonds within the molecule.

* These N₂ molecules interact with each other through weak London dispersion forces, which are responsible for its solid state at low temperatures.

Other types of crystalline solids:

* Ionic solids are formed by electrostatic attractions between oppositely charged ions.

* Metallic solids are formed by metallic bonds, where electrons are delocalized throughout the solid.

* Covalent network solids are formed by covalent bonds extending throughout the entire structure.

Since nitrogen does not form ions or have delocalized electrons, it does not fit into the categories of ionic, metallic, or covalent network solids.