chemistry ions, isoelectronic series

Question

Considering only ions with charges of +1, +2, -1 and -2, or neutral atoms, give the symbols for 4 species that are isoelectronic with Kr

Answer 1

Answer: Br^-, Se^2-, Rb⁺, Sr²⁺

Find Kr in the periodic table.

Move one element to the left. You will see Br. If you add 1 electron to Br you get Br^-which is isoelectronic with Kr

Move 2 elements to the left. You will see Se. If you add 2 electrons to Se you get Se^2- which is isoelectronic with Kr

Move one element past Kr and you will find Rb. Remove 1 electron to get Rb⁺ which is isoelectronic with Kr.

Move 2 elements past Kr and find Sr. Remove 2 electrons to get Sr²⁺ which is isoelectronic with Kr.