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

The number of unpaired electrons is determined by the electronic configuration and Hund's rule. Boron (atomic number 5) has the configuration 1s² 2s² 2p¹, resulting in one unpaired electron in the 2p orbital. Nitrogen (atomic number 7) has the configuration 1s² 2s² 2p³; 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 1s² 2s² 2p⁴; 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 (1s² 2s² 2p⁶), 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 – 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