Q. Which of the following represents the correct order of increasing first ionisation enthalpy for $Ca, Ba, S, Se$ and $Ar$ ?
Solution:
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
Group No. 2
16
18
Ca
S
Ar
Ba
Se
Thus, the order of increasing $\Delta H_{IE_1}$ is
$Ba< Ca< Se< S< Ar$
| Group No. 2 | 16 | 18 |
|---|---|---|
| Ca | S | Ar |
| Ba | Se |
