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Q63 (CAPF/2024) Science & Technology ā€ŗ Basic Science (Physics, Chemistry, Biology) ā€ŗ Periodic table elements

Match List I with List II and select the correct answer using the code given below the Lists: List I (Element) A. Boron B. Nitrogen C. Oxygen D. Neon List II (Unpaired electron) 1. Zero 2. Two 3. One 4. Three

Result
Your answer: ā€”  Ā·  Correct: D
Explanation

The number of unpaired electrons is determined by the electronic configuration and Hund's rule. Boron (atomic number 5) has the configuration 1sĀ² 2sĀ² 2pĀ¹, resulting in one unpaired electron in the 2p orbital. Nitrogen (atomic number 7) has the configuration 1sĀ² 2sĀ² 2pĀ³; according to Hund's rule, each of the three 2p orbitals is occupied by a single electron, giving it three unpaired electrons [1]. Oxygen (atomic number 8) has the configuration 1sĀ² 2sĀ² 2pā“; the eighth electron pairs with one in the 2p orbital, leaving two unpaired electrons. Neon (atomic number 10) is a noble gas with a completely filled valence shell (1sĀ² 2sĀ² 2pā¶), meaning all its electrons are paired, resulting in zero unpaired electrons [2]. Matching these gives: A-3, B-4, C-2, D-1.

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON ā€“ 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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