Question

Which atom and/or ion is (are) isoelectronic with$\begin{array}{r}\mathbf{B}{\mathbf{r}}^{+}:\mathbf{S}{\mathbf{e}}^{\mathbf{2}+},\mathbf{S}\mathbf{e},\mathbf{A}{\mathbf{s}}^{-}-,\mathbf{K}\mathbf{r},\mathbf{G}{\mathbf{a}}^{\mathbf{3}+},\mathbf{C}{\mathbf{l}}^{-}-?\\ \end{array}$

Short answer

Se and$A{s}^{-}$ are isoelectronic with Br⁺

Step-by-step solution

Isoelectronic species

An atom is isoelectronic with another if they both have the same number of total electrons. In other words, isoelectronic atoms/ ions are atoms with the same electron configuration.

Ions/atoms that are isoelectronic with Br+    

Valence shell electronic Configuration of Br⁺= 4p⁴

Configuration of elements given in the question

$\begin{array}{r}S{e}^{2+}=4p^2\\ Se=4p^4\\ A{s}^{-}=4p^4\\ Kr=4p^6\\ G{a}^{3+}=3d^{10}\\ C{l}^{-}=3p^5\end{array}$

Observing the given configuration, we can conclude that Se and$\mathbf{A}{\mathbf{s}}^{-}$ are isoelectronic with$\mathbf{B}{\mathbf{r}}^{+}$.