$S_1$  : Among $K^{+}$ , $M{g}^{2+}$ and $A{l}^{3+}$ ions $A{l}^{3+}$is the smallest one.

$S_2$ : The negative value of electron gain enthalpy of $Cl>F$ because there is weak electron-electron repulsion in the bigger 3p-sub shell of Cl as compared to compact 2psubshell of F.

$S_3$ :Formation of $S^{2-}$ and $A{r}^{-}$ ,both require the absorption of energy

$S_4$ : The following set of elements represent the incorrect order of magnitude of electron gain enthalpy values  $\mathrm{S}>\mathrm{O}$