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
Order of increasing `DeltaH_(IE_(1)) : Ba lt Ca lt Se lt S lt Ar`
`Ba lt Ca , Se lt S:` On moving top to bottom in a group, size increases. So ionisation enthalpy decreases `Ar`: Maximum value of ionisation enthalpy, since it is an inert gas.