Second electron gain enthalpy : — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Step 1: The second electron gain enthalpy is the energy change associated with adding an electron to a gaseous uni-negative ion (X^- + e^- -> X^2-). Step 2: Adding a negatively charged electron to an already negatively charged anion results in strong electrostatic repulsion. Step 3: Energy must be absorbed to overcome this mutual repulsion, making the process highly endothermic. Thus, the second electron gain enthalpy is always positive (option b).