EASYMCQ SINGLEIChO (Chemistry Olympiad)Physical ChemistryAtomic StructureIntro

[NEET 2021] From the following pairs, which one is NOT an isoelectronic pair?

0.Mn²⁺, Fe³⁺

1.Fe²⁺, Mn²⁺

2.O²⁻, F⁻

3.Na⁺, Mg²⁺

Explanation

Mn²⁺: 25−2=23 e⁻; Fe³⁺: 26−3=23 e⁻ → isoelectronic ✓. Fe²⁺: 26−2=24 e⁻; Mn²⁺: 25−2=23 e⁻ → NOT isoelectronic ✗. O²⁻: 8+2=10; F⁻: 9+1=10 ✓. Na⁺: 11−1=10; Mg²⁺: 12−2=10 ✓.

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