Which of the following represents an excited state of an atom? — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Step 1: Ground state configurations are determined by filling orbitals of lowest energy first (Aufbau principle). Options (a), (b), and (c) represent the ground states of Nickel, Chromium (an stable half-filled exception), and Scandium respectively. Step 2: Examine the configuration 1s2 2s2 2p5 3s1. The 2p subshell is not fully filled (it can hold 6 electrons), yet an electron has been promoted to the higher energy 3s subshell. Step 3: This promotion of an electron to a higher energy orbital prior to filling the lower energy subshell is a signature of an excited state (specifically, an excited state of a Fluorine atom).