Here's why:

* Monatomic: Means a single atom. Chlorine exists as Cl2, meaning it's two chlorine atoms bonded together.

* Lattices: Refers to a repeating, ordered arrangement of atoms or molecules in a solid structure. While chlorine can form solid lattices (like in table salt, NaCl), chlorine gas itself does not exist as a lattice.

Key takeaway: Chlorine exists as a diatomic molecule (Cl2) in its gaseous form, which is the most common state at room temperature and pressure.