JEE Main 2013 — Classification of Elements and Periodicity in Properties Question with Solution

$\mathrm{Ba} < \mathrm{Ca} < \mathrm{Se} < \mathrm{S} < \mathrm{Ar}$

Ba and Ca belong to group IIA ( alkaline earth metals).

Se and S belong to group Vl A (Chalcogens) and as we go down the group ionization enthalpy decreases with increasing atomic size. So,
         
          $\mathrm{Ba} < \mathrm{Ca} \text{and } \mathrm{Se} < \mathrm{S}$
Ar has stable completely filled electronic configuration and, therefore, has the highest ionization enthalpy.Hence, the correct order is

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