Which of the following represents the correct increasing order of the first ionization enthalpies () — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Boron ($B$, period 2, group 13) has the lowest $IE_1$ among the choices. Across period 3, Phosphorus ($P$) has a higher $IE_1$ than Sulphur ($S$) due to the extra stability of its half-filled $3p^3$ subshell compared to $S$'s $3p^4$. Fluorine ($F$, period 2, group 17) has the smallest size and highest $Z_{eff}$, giving it the highest $IE_1$. Thus, the order is $B < S < P < F$.