Formation of Cl- ion is exothermic whereas O2- ion formation is endothermic. — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Step 1: Write down the electronic configuration for each element to determine the number of unpaired electrons in their ground states. Step 2: Nitrogen (N: 1s2 2s2 2p3) has 3 unpaired electrons; Oxygen (O: 1s2 2s2 2p4) has 2 unpaired electrons; Aluminum (Al: [Ne] 3s2 3p1) has 1 unpaired electron; Calcium (Ca: [Ar] 4s2) has 0 unpaired electrons. Step 3: Paramagnetic behavior increases with the number of unpaired electrons. Therefore, the correct decreasing order of paramagnetism is N (3) > O (2) > Al (1) > Ca (0).