Which of the following ions is not isoelectronic with the noble gas argon?

Question

Quizplus · Accepted Answer

Isoelectronic means having the same number of electrons as the noble gas argon. Argon has 18 electrons. 
A) S₂- has 18 electrons (16 + 2 = 18), so it is isoelectronic with argon. 
B) Cl- has 18 electrons (17 + 1 = 18), so it is isoelectronic with argon. 
C) K+ has 18 electrons (19 - 1 = 18), so it is isoelectronic with argon. 
D) SC₃+ has 15 electrons (16 - 3 = 13), so it is not isoelectronic with argon. 
E) V4+ has 22 electrons (23 - 4 = 19), so it is not isoelectronic with argon.

Which of the Following Ions Is Not Isoelectronic with the Noble