Explanation:
The highest occupied energy sub-level is defined as number of electrons present in the outermost energy level of an atom.
For example, for alkali metals general electronic configuration is [tex]ns^{1}[/tex].
This means that in the highest occupied energy sub-level of an alkali metal there will be only one electron.
Whereas for alkaline earth metals general electronic configuration is [tex]ns^{2}[/tex]. This means there are 2 electrons present in the highest occupied energy sub-level of an alkaline earth metal.
Thus, we can conclude that atom that contains only one electron in the highest occupied energy sublevel are alkali metals.
