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🧪 Chemistry  ·  Classification of Elements and Periodicity in Properties  ·  NEET & JEE

The isoelectronic series O<sup>2-</sup>, F-, Ne, Na+, Mg<sup>2+</sup> all have 10 electrons. Their ionic radii decrease because:

Answer: Increasing nuclear charge attracts the same 10 electrons more strongly.

  • A Increasing nuclear charge attracts the same 10 electrons more strongly
  • B Each successive species actually has fewer than 10 electrons according to conventional understanding
  • C Electron shielding increases steadily across the series in routine practice
  • D Each species occupies a different number of electron shells overall

Correct answer: A. Increasing nuclear charge attracts the same 10 electrons more strongly

Explanation: Same electron count (10), but Z increases from 8 (O) to 12 (Mg); greater nuclear charge compresses the electron cloud.

The complete modern periodic table showing all 118 elements with atomic number, symbol, and atomic mass, color-coded by element category

The complete modern periodic table (118 elements). Image: Cepheus et al., Public Domain, via Wikimedia Commons.

Concept context

The periodic table organises all 118 elements by atomic number and similar properties. Study periodic trends like atomic radius, ionization energy, and electronegativity, and learn how an element's position predicts its behaviour.

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