Question

An element belongs to group 15 and third period of the periodic table, its electronic configuration will be
A.${\text{1}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{p}}^{\text{3}}}$
B.${\text{1}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{p}}^4}$
C.${\text{1}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{p}}^6}{\text{3}}{{\text{s}}^{\text{2}}}{\text{3}}{{\text{p}}^{\text{3}}}$
D.${\text{1}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{p}}^6}{\text{3}}{{\text{s}}^{\text{2}}}{\text{3}}{{\text{p}}^2}$

Answer 1

Group number indicates the electrons present in the outermost valence shell. Period number indicates the principal quantum number of the outermost shell.

Complete answer:
The elements of group 15 have five electrons in the outermost valence shell.
The third period indicated that the outermost shell has principal quantum number 3.

So, the electronic configuration of the element is as follows:
${\text{1}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{p}}^6}{\text{3}}{{\text{s}}^{\text{2}}}{\text{3}}{{\text{p}}^{\text{3}}}$
The option (A) shows that the electrons in the outermost shell are five but the principal quantum number of the outermost shell is two so, the option (A) is incorrect.
The option (B) shows that the electrons in the outermost shell are six and the principal quantum number of the outermost shell is two so, the option (B) is incorrect.
The option (C) shows that the electrons in the outermost shell are five and the principal quantum number of the outermost shell is three so, the option (C) is correct.
The option (B) shows that the principal quantum number of the outermost shell is three but the electrons in the outermost shell are four so, the option (D) is incorrect.

Hence the correct answer is (C).

Note: The outer electronic configuration of an element tells us about the group number from which it belongs. If we know the atomic number of an element we can easily write the electronic configuration and find out the group number or period from which it belongs.