Helium atom has highest ionisation energy among all the elements. — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Step 1: Understand that electropositive character (metallic character) increases moving down a group and decreases moving from left to right across a period. Step 2: Alkali metals (Group 1) are always more electropositive than alkaline earth metals (Group 2) within the same period due to lower ionization energies. Step 3: Among the choices, [He] 2s1 (Lithium) and [Xe] 6s1 (Cesium) are alkali metals. Since Cesium is much further down Group 1 than Lithium, its outermost electron is most easily lost, making [Xe] 6s1 the configuration of the most electropositive element.