Question

Alkaline earth (group 2 or IIA elements) differ from group 12 (or IIB) elements in the electronic configuration of their:
A. Antepenultimate
B. Innermost shell
C. Outermost shell
D. Penultimate shell

Answer 1

Hint: The last shell of nucleus or outermost shell is known as the valence shell. The shell inside the valence shell is known as the penultimate shell and the one shell that is inside to penultimate is known as the anti-penultimate shell or pre-penultimate shell.

Complete answer
The Alkaline earth (group 2 or IIA elements) are called alkaline earth metals because theses metals form alkaline solutions (i.e, hydroxides) when these metals are reacted with water .So basically, this term alkaline means that the solution has a pH greater than seven value and is basic in nature. Thus, the alkaline earth metals form solutions which are basic in nature and are extremely effective as best reducing agents.
The elements in group twelve are not transition elements because the last electron added to their shell is not a d electron, but an s electron. As the last electron added is an s electron, these elements are known as representative metals or post-transition metals.
Electronic configuration Alkaline earth (group 2 or IIA elements) elements is \[n{s^2}\]
Electronic configuration group 12 (or IIB) elements is \[n{s^2},(n - 1){d^{10}}\],
So these two groups differ in their electronic configuration of the penultimate shell.

Therefore, the correct answer is option D. Penultimate shell.

Note:
The nuclear charge q increases as we go from group one to group two. Because of this increase in nuclear charge, the atoms of the alkaline earth metals are smaller and have higher ionization energies than the alkali metals i.e, group one within the same period and the group twelve elements behave much like the alkaline earth metals of group two than transition metals.