The following are isoelectronic ions except?

A. Na+
B. Mg²+
C. Si²+
D. O²+

Correct Answer:

Option C – Si²+

Explanation

Two or more ions are said to be isoelectronic if they have the same electronic structure and the same number of valence electrons.

Na+ = 10 electrons = 2, 8

Mg²+ = 10 electrons = 2,8

O²− = 10 electrons = 2,8

Si²+ = 12 electrons = 2,8,2

⟹ Si²+ is not isoelectronic with the rest.