Which one of the following sets of ions represents a collection of isoelectronic species?

(Atomic numbers: F = 9, Cl = 17, Na = 11, Mg = 12, Al = 13, K = 19, Ca = 20, Sc = 21)

Question

Which one of the following sets of ions represents a collection of isoelectronic species?

(Atomic numbers: F = 9, Cl = 17, Na = 11, Mg = 12, Al = 13, K = 19, Ca = 20, Sc = 21)

Canvas Classes · Accepted Answer

Option (4):

| Ion | Z | Charge | Electrons |
|-----|---|--------|-----------|
|  | 19 | +1 | 18 |
|  | 17 | −1 | 18 |
|  | 20 | +2 | 18 |
|  | 21 | +3 | 18 |

All have 18 electrons (Ar configuration) ✓

Others fail: (1) Li⁺ has 2e⁻; (2) Ba²⁺ has 54e⁻; (3) S²⁻ has 18e⁻ vs N³⁻/O²⁻/F⁻ with 10e⁻.

Answer: Option (4)

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