Question

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

Answer 1

Correct Answer - C
Ionisation energy increases along a period from left to right and decreases down a group. The position of given elements in the periodic table is as
` {:(2,16,18),(Ca,S,Ar),(Ba,Se,):}`
Thus, the order of increasing `DeltaHIE_(1)` is
`Ba lt Ca lt Se lt S lt Ar`.