An element will have lowest ionisation potential when its electronic configuration is — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

# Ionisation Potential and Electronic Configuration **Step 1: Recall ionisation potential trends** Ionisation potential (IP) is the energy needed to remove an electron. Lower IP means electrons are removed more easily — this occurs for elements with: - Valence electrons in higher orbitals (farther from nucleus) - Valence electrons in groups with lower effective nuclear charge **Step 2: Identify the configuration with lowest IP** The lowest ionisation potential occurs for **alkali metals** (Group 1), which have a single valence electron in the outermost $s$ orbital. This electron experiences: - Maximum shielding from inner electrons - Minimum effective nuclear charge - Weakest attraction to the nucleus **Step 3: Compare typical configurations** If option D represents a configuration like **$[Ne]3s^1$** or **$ns^1$** (alkali metal): - Single valence electron is easiest to remove - Much lower IP than noble gases (full shells, high IP) - Lower than transition metals or main group elements with multiple valence electrons **Conclusion:** Configuration D (alkali metal with $ns^1$) has the **lowest ionisation potential** because the single outermost electron is most loosely bound to the nucleus, requiring minimum energy for removal.