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Q20 (NDA-I/2012) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Basic chemical principles Answer Verified

Which one among the following is correct regarding 20Ne, 23Na+, 19F- and 24Mg2+?

Result
Your answer: —  Â·  Correct: C
Explanation

The species 20Ne, 23Na+, 19F-, and 24Mg2+ are isoelectronic because they all possess exactly 10 electrons. Isoelectronic species are defined as chemical entities having the same number and configuration of electrons. Neon (Ne) has an atomic number of 10, meaning it naturally has 10 electrons [1]. Sodium (Na) has 11 electrons, but the Na+ cation loses one electron from its outermost shell, leaving it with 10 [2]. Fluorine (F) has 9 electrons, but the F- anion gains one electron to complete its octet, resulting in 10 electrons [1]. Magnesium (Mg) has 12 electrons, and the Mg2+ cation loses two electrons to attain a stable noble gas configuration of 10 electrons [3]. Since they do not share the same atomic number, they are not isotopes. Thus, they are isoelectronic with each other.

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.3 HOW DO METALS AND NON-METALS REA ALS REACT? > p. 47
  2. [2] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.3 HOW DO METALS AND NON-METALS REA ALS REACT? > p. 46
  3. [3] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON – THE COVALENT BOND > p. 59
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