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Q60 (CDS-I/2025) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Basic chemical principles Answer Verified

Number of electrons present in the species H2, He, H2 and O2 respectively are :

Result
Your answer: —  Â·  Correct: C
Explanation

The number of electrons in a species is determined by its atomic number and molecular composition. A neutral hydrogen atom has an atomic number of 1, meaning it contains one electron [1]. Consequently, a hydrogen molecule (H2) consists of two hydrogen atoms sharing electrons, resulting in a total of 2 electrons [1]. Helium (He) is a noble gas with an atomic number of 2, thus a single helium atom contains 2 electrons in its filled K shell [2]. Oxygen (O) has an atomic number of 8, meaning a neutral oxygen atom has 8 electrons. Therefore, a diatomic oxygen molecule (O2) contains a total of 16 electrons (8 x 2). Based on these calculations, the number of electrons for H2, He, H2 (repeated in query), and O2 are 2, 2, 2, and 16 respectively, which corresponds to option 3.

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON – THE COVALENT BOND > p. 59
  2. [2] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON – THE COVALENT BOND > p. 60
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