As far as I can tell the best answer for this would be (A) Neon. However, I would argue that this is at the very least a misleading question. Atoms are less identified by their electrons than their protons (which is represented always by its atomic number). Although atoms can gain or lose electrons, the protons would never change (and remain the same element). Personally, I would have written the question as, "When Magnesium loses its valence electrons, its new number of electrons would most closely resemble _____"