What is the type of this electron behavior?
To understand the electrons' behavior, we need to understand the differences between the electrons of a metal and a non-metal. Both metals and non-metals have valence electrons, but while the metals are the likely donors, non-metals are generally the electron acceptors. In this process we end up with ionic compounds. Also, in general, metals are less electronegative than non-metals and hence are not as capable of pulling electrons towards them. Electrons can also be shared among atoms to form covalent bonds.
In the given scenarios, presence of only non-metals implies that no electron donors are present and electrons can only be shared among non-metallic atoms. Imagine chlorine gas, Cl_2, where only chlorine atoms are required. Electrons in such system are probably shared. In the case of bonding between metals and non-metals (ionic bonding to be more precise), electrons have been donated by metals, accepted by non-metals and electroneutrality is there, i.e. no free electrons are there. When we have a mixture of metals and non-metals, electrons (in simplest terms) would be moving from metal atoms towards non-metal atoms in order to form ionic bonds. When only metals are present in the system, there are no acceptors and electrons will either be attached to atoms or (if cations are already formed) they will be freely moving around. This seems to be the case in the image, so D is the right answer, representing the delocalization of electrons from the metal atoms.
Hope this helps.