The lowest atomic number ion is Se^2-.
The highest atomic number ion is Sr^2+.
The ones in the middle are NOT Br^- or Rb^+. However, I do not know what the correct answer for those two is.
Pallidium
The noble gas configuration of technetium is [Kr] 4d^5 5s^2.
The element with the electron configuration Kr 5s^2 4d^10 5p^2 is Xenon (Xe).
The element with an electron configuration of Kr 4d^6 corresponds to the element Palladium (Pd).
The element E is likely barium (Ba), as its electron configuration is Kr 5s2. The fluoride compound of barium would be BaF2, with barium losing its two valence electrons to form a 2+ cation and fluoride gaining one electron to form a 1- anion.