Question

Maximum number of covalent bonds formed by $N$ and $P$ are:
A. $3,{\text{ }}5$
B. $3,{\text{ }}6$
C. $3,{\text{ }}4,{\text{ }}5$
D. $3,{\text{ }}4,{\text{ }}6$

Answer 1

The valency of an element is calculated by the electronic configuration of that element. The number of covalent bonds formed by an element is called the covalency of that element.

Complete step by step answer:
Two words have to understand first to answer the given question of which one is valency and the other is covalency. Valency is the number of electrons which are lost or gained during the formation of an ionic or covalent bond. Covalency is the number of covalent bonds formed by a certain element using all the valence electrons in $s,{\text{ }}p,{\text{ }}d{\text{ }}and{\text{ }}f$ orbitals.
Hence valency does not depend on the number of valence electrons but covalency depends on the number of valence electrons. Covalency refers to the maximum number of covalent bonds formed by an atom.
Nitrogen atoms are designated by the symbol $N$. It is an element in the periodic table with atomic number $7$. Its electronic configuration is $\left[ {He} \right]2{s^2}2{p^3}$ . The outermost shell of nitrogen is $2$ and has five electrons present in it. Of these two electrons are present in $2s$ orbital and three electrons are present in $2p$ orbital.
As the number of valence electrons of nitrogen is five and to attain the octet configuration so it can accept or lose $3$ electrons. Thus the maximum number of covalent bonds formed by $N$ is $3$.
Phosphorus atom is designated by the symbol $P$. It is an element in the periodic table with atomic number $15$. Its electronic configuration is $\left[ {Ne} \right]3{s^2}3{p^3}$. The outermost shell of phosphorus is $3$ and has five electrons present in it. Of these two electrons are present in $3s$ orbital and three electrons in $3p$ orbital. Besides this phosphorus also contains $3d$ orbital as outer orbital and can use this for making covalent bonds. Thus the maximum number of covalent bonds formed by $P$ is $5$.
And hence option A is the correct answer.

Note:
The availability of outer $d$ orbitals in elements down the group enables the element to extend the covalency of the elements and form more number of bonds.