Chapter 7.6, Problem 1CP

Which of the following species are isoelectronic with Kr? (Select all that apply.)

$\begin{array}{l}\text{a)}\hfill \\ \text{He}\hfill \\ \text{b)}\hfill \\ \text{Ne}\hfill \\ \text{c)}\hfill \\ \text{Ar}\hfill \\ \text{d)}\hfill \\ \text{Br­}\hfill \\ \text{e)}\hfill \\ {\text{Rb}}^{\text{+}}\hfill \end{array}$