Which electronic configuration must represent an atom in an excited state? — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Step 1: Recall the Aufbau principle, which states that electrons fill lower-energy orbitals before filling higher-energy ones in the ground state. Step 2: In options (a), (b), and (d), the orbitals are filled sequentially in their ground state configuration. In (c), an electron has been promoted from the 2p orbital to the higher-energy 3s orbital before the 2p subshell is filled. Step 3: Conclude that the configuration 1s2 2s2 2p2 3s1 represents an excited state of a Nitrogen atom (option c).