Most of the monatomic ions of the representative elements are obtained by removing all the valence electrons from the atoms of metallic elements. Once these atoms have lost their valence electrons, they have stable noble gas or pseudo noble gas configurations.
Which of these elements forms a cation having pseudo noble gas configuration?

Options

A. `Mg`
B. `Ga`
C. `K`
D. `Al`

Answer

B

Explanation

Electronic configurations of alkali metals such as K consist of a noble gas core (i.e., an inner-shell configuration corresponding to one of the noble gases) plus one outermost electron. Configurations of alkaline earth metals (such as Mg) consist of a noble gas core plus two outermost electrons. Al has a noble gas core plus 3 outermost electrons. `Ga([Ar]3d^(10)4s^2 4p^1)` has an additional filled 3d subshell. The noble gas core together with `(n-1)d^(10)` electrons is often referred to as a pseudo noble gas core, because these electrons usually are not involved in chemical reactions.