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

Options

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

Answer

C

Explanation

Ionisation energy increases along a period from left to right and decreases down the group.