1. Understand Isoelectronic

Isoelectronic species have the same number of electrons.

2. Barium Ion

Barium (Ba) is in group 2 of the periodic table, so it forms a +2 ion: Ba²⁺.

3. Electron Configuration

* Barium's electron configuration: [Xe] 6s²

* Barium ion (Ba²⁺) electron configuration: [Xe]

4. Find Ions with the Same Electron Configuration

To find isoelectronic ions, look for elements that, after forming ions, will have the same electron configuration as the barium ion ([Xe]).

* Iodine ion (I⁻): Iodine (I) is in group 17 and gains one electron to form I⁻. Its electron configuration becomes [Xe].

* Cesium ion (Cs⁺): Cesium (Cs) is in group 1 and loses one electron to form Cs⁺. Its electron configuration becomes [Xe].

* Xenon (Xe): Xenon is a noble gas and already has the [Xe] electron configuration.

Therefore, the ions isoelectronic with the barium ion (Ba²⁺) are:

* Iodine ion (I⁻)

* Cesium ion (Cs⁺)

* Xenon (Xe)