Answers

a. aluminum, Z=13

Al⁺³: 1s²2s²2p⁶ it has the same configuration as Ne

b. bromine, Z=35

Br^- : 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶ it has the same configuration as Kr

c. calcium, Z=20

Ca²⁺: 1s²2s²2p⁶3s²3p⁶ it has the same configuration as Ar

d. lithium, Z=3

Li⁺¹ : 1s² it has the same configuration as He

e. fluorine, Z=9

F^- : 1s²2s²2p⁶ it has the same configuration as Ne