Which of the following pairs has a higher ionization enthalpy?
$(i)$ $Ne$ or $Ar$ $(ii)$ $Cl$ or $F$ $(iii)$ $F$ or $O$ $(iv)$ $N$ or $O$
$(v)$ $Na$ or $K$ $(vi)$ $Cl$ or $S$ $(vii)$ $Kr$ or $Xe$ $(viii)$ $P$ or $S$

(A) Ionization enthalpy generally increases across a period and decreases down a group.
$(i)$ $Ne > Ar$ (Down the group,size increases,$IE$ decreases).
$(ii)$ $F > Cl$ (Down the group,size increases,$IE$ decreases).
$(iii)$ $F > O$ (Across the period,effective nuclear charge increases,$IE$ increases).
$(iv)$ $N > O$ ($N$ has a stable half-filled $2p^3$ configuration,making its $IE$ higher than $O$).
$(v)$ $Na > K$ (Down the group,size increases,$IE$ decreases).
$(vi)$ $Cl > S$ (Across the period,effective nuclear charge increases,$IE$ increases).
$(vii)$ $Kr > Xe$ (Down the group,size increases,$IE$ decreases).
$(viii)$ $P > S$ ($P$ has a stable half-filled $3p^3$ configuration,making its $IE$ higher than $S$).