Which substance involves no bonding forces EXCEPT London (dispersion) forces?

Little more explanation. Covalent bonding like in N2 you got. Ionic bonding like NaCl check. Metals are really different type beasties. There are no metal-metal compounds because both of the metals are wanting to give up electrons and don't want to take or share any electrons. So what happens in a metal? Picture all of these metal atoms in a fixed 3-dimensional array (what we call a crystal, or if amorphous, just a mass gathering) none of these atoms particularly wants to hold onto the valence electrons, so they become a resource that is owned by the community. In other words the electrons are allowed to wander around the neighborhood. This is called the "sea of electrons" model (check it out on a browser) and helps explain some of the behavior of metals, like electrical conduction - if extra electrons are introduced at one end of the array, an electrical imbalance is produced that can only be satisfied if electrons exit the other end.