Chemistry - PERIODIC TABLE Question with Solution | TestHub

Ba < Ca < Se < S < Ar

Ba,  Ca belong to gr IIA ( alkaline earth metals)

Se and S belong to gr Vl A (Chalcogens)
and as we go down the group ionaization enthalpy decreases with increasing atomic size. So,

Ba < Ca      and
Se < S

Ar has stable completely filled electronic configuration and, therefore,has higest ionization enthalpy.Hence,the correct order is

$\begin{array}{cccccccccc}& \text{Ba}& <& \text{Ca}& <& \text{Se}& <& \text{S}& <& \text{Ar}\\ {\text{in kJmol}}^{-1}& 503& & 590& & 941& & 999& & 1520\end{array}$