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Which of the following groups does not consist of isoelectronic species?

1. BO₃³⁻, CO₃²⁻, NO₃⁻
2. SO₃²⁻, CO₃²⁻, NO₃⁻
3. CN⁻, N₂, C₂²⁻
4. PO₄³⁻, SO₄²⁻, ClO₄⁻

Correct answer: SO₃²⁻, CO₃²⁻, NO₃⁻

Solution

SO3^2- has 42 electrons while CO3^2- and NO3^- have 32 each, so set (option 1) is NOT isoelectronic. The stored set PO4^3-/SO4^2-/ClO4^- all have 50 electrons (isoelectronic), so it is not the answer.

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