Explanation:
Al3+ has 10 electrons. The electronic configuration is;
1s² 2s² 2p⁶
Ba2+ has 54 electrons. The electronic configuration is;
1s² 2s² 2p6 3s² 3p⁶ 3d10 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶
Br- has 37 electrons. The electronic configuration is;
1s² 2s² 2p6 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶
O2- has 10 electrons. The electronic configuration is;
1s² 2s² 2p⁶
