Which of the following represents the correct order of increasing first ionisation enthalpy for `Ca,Ba,Se`, and `Ar`?

Options

A. `ba lt Ca lt Se lt S lt Ar`
B. `Ca lt S lt Ba lt Se lt Ar`
C. `Ca lt Ba lt S lt Se lt Ar`
D. `S lt Se lt Ca lt Ba lt Ar`

Answer

A

Explanation

`|{:("Group",---,Group ,----,Group),(2,,16,,18),(Mg,,S,,Ar),(Ca,,Se,,),(Sr,,,,),(Ba,,,,):}:|`
In general, the ionization enthalpy increases across the period due to increase of `Z_(eff)` while it decreases down the group due to increasing size. Thus, `Ba` lying the lowest in the periodic table has the minimum ionization enthalpy while `Ar` (a noble gas) lying to the extreme right has the maximum ionization enthalpy. Thus, the correct order is
`Ba lt Ca lt Se lt S lt Ar`