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Q12 (NDA-II/2018) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Basic chemical principles Answer Verified

The atomic number of an element is 8. How many electrons will it gain to form a compound with sodium?

Result
Your answer: —  Â·  Correct: B
Explanation

The element with atomic number 8 is oxygen [1]. Its electronic configuration is 2, 6, meaning it has six electrons in its outermost (L) shell [1]. To achieve a stable noble gas configuration (an octet), oxygen requires two additional electrons [1]. Sodium, with atomic number 11, has one electron in its outermost shell and tends to lose it to form a Na+ cation [2]. When sodium reacts with oxygen to form an ionic compound like sodium oxide (Na2O), each sodium atom loses one electron, and the oxygen atom gains a total of two electrons to form an O2- anion. This transfer allows oxygen to complete its valence shell, attaining the stable configuration of neon. Therefore, oxygen gains two electrons to bond with sodium.

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON – THE COVALENT BOND > p. 60
  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. 47
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