Final answer:
The species F-, Na+, and Mg2+ are isoelectronic with each other because they all have the same electron configuration as the noble gas neon (Ne) after gaining or losing electrons, whereas O2 is not isoelectronic as it has a different electron count.
Step-by-step explanation:
The species that are isoelectronic with each other are those that have the same number of electrons. Isoelectronic species have the same electron configuration, although they may have different numbers of protons. An example of isoelectronic species is when we consider the noble gas neon (Ne), which has an electron configuration of 1s²2s²2p⁶. From the given options, F- and Na+ are both isoelectronic with neon because when fluorine gains an electron, it achieves this configuration, and when sodium loses an electron, it also achieves the same electron configuration. Mg²+ also has the same number of electrons as neon. However, molecular oxygen (O₂) has a different electron count and is not isoelectronic with these ions.