WAEC - Chemistry (2012 - No. 3)

Which of the following ions has an electron configuration different from the other?

₁₇CI^-

₈O^2-

₁₂Mg²⁺

₁₃AI³⁺

\(_{17}\)Cl\(^-\) = 18 electrons = 2, 8, 8

\(_{12}\)Mg\(^{2+}\), \(_{8}\)O\(^{2-}\) and \(_{13}\)Al\(^{3+}\) all have 10 electrons = 2, 8.