Which of the following sets of elements correctly represents the increasing order of their first ion — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Across a period, $IE$ generally increases. Period 2 elements generally have higher $IE$ than period 3. Boron is lowest ($2s^2 2p^1$). Between Sulphur and Phosphorus (Period 3), $P$ ($3s^2 3p^3$) is half-filled and more stable than $S$ ($3s^2 3p^4$), so $P > S$. Fluorine ($2s^2 2p^5$) has the highest $Z_{eff}$ and is smallest. The correct increasing order is $B < S < P < F$.