JEE Main · 2023 · 25 Jan 2023 · Shift 1 · Classification of Elements and Periodicity

A noble gas already has a closed shell, so an added electron must enter the next higher shell and is resisted, making every electron gain enthalpy positive. The size of this positive value grows as the valence region grows more compact and repels the incoming electron more strongly: neon, the most compact of these, resists most and shows the largest value, followed by krypton and then xenon, while helium shows the smallest positive value of all. Arranged in increasing order the electron gain enthalpies run helium, xenon, krypton, neon.