Question

The species which have same number of electrons in outermost and penultimate shell –
(A) $Ca$
(B) $Ar$
(C) ${V^{ + 3}}$
(D) $S{c^{3 + }}$

Answer 1

Hint : To answer this question, we first need to understand what electrons are. Electrons are negatively charged atom particles. The negative charge created by all of an atom's electrons balances the positive charge of the protons in the atomic nucleus. Electrons are quite little in comparison to the rest of the atom.

Complete Step By Step Answer:
Outer most shell - The number of electrons in an atom's outermost shell impacts its reactivity, or its proclivity for forming chemical connections with other atoms. The valence shell is the outermost shell, and the electrons in it are known as valence electrons.
Penultimate shell - The penultimate shell is the one that is filled shortly before the valence shell, that is, the one that is closest to the valence shell. It will be one less than valence shell in terms of number. The penultimate shell will have value if the valence shell has value 'n' (n-1). Magnesium, for example, has an atomic number of 12.
$\ Electronic{\text{ }}distribution{\text{ }}of{\text{ }}Ca{\text{ }} - 1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^2} \\\ Electronic{\text{ }}distribution{\text{ }}of{\text{ Ar }} - 1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}. \\\ Electronic{\text{ }}distribution{\text{ }}of{\text{ }}{{\text{V}}^{ + 3}}{\text{ }} - 1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^0}3{d^2} \\\ Electronic{\text{ }}distribution{\text{ }}of{\text{ S}}{{\text{c}}^{3 + }}{\text{ }} - 1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}$
From this we can observe that $S{c^{3 + }}$ have same number of electrons in the outermost and penultimate shell.
So, the final answer is option (D) i.e., $S{c^{3 + }}$ .

Note :
The electron configuration is the distribution of electrons in atomic or molecular orbitals of an atom or molecule (or other physical structure) in atomic or molecular physics and quantum chemistry. Each electron is described as travelling independently in an orbital in an average field created by all other orbitals in electronic setups. Configurations are described mathematically by Slater determinants or configuration state functions.