Question

The valency of phosphorus in ${H_3}P{O_4}$ is:
A. 2
B. 5
C. 4
D. 1

Answer 1

Hint: The valency of an element refers to the measure of combining capacity of the atom with other atoms while forming a chemical compound or molecule. In other words, the maximum number of bonds that an atom can form while forming a chemical compound is referred to as its valency.

Complete answer:
The chemical name of the given compound i.e., ${H_3}P{O_4}$ is phosphoric acid which is a very weak acid and at pure state, it is a colourless solid. Like carboxylic acids, these acids have tendency to dimerize via dehydration reaction to form phosphoric-anhydrides. Phosphoric acid is referred to as tribasic because it has a total of three possibilities of dissociation.
Structurally, ${H_3}P{O_4}$ can be represented as follows:

As from the structure, it is clear that the number of bonds formed by the phosphorus atom in phosphoric acid is 5.
Number of electrons in the valence shell of an atom also represents the valency of that atom. So, the electronic configuration of phosphorus is $[Ne]3{s^2}3{p^3}$. As the number of electrons in the valence shell of phosphorus are 5.
Thus, we can conclude that the valency of phosphorus in ${H_3}P{O_4}$ is 5.

Note:
It is important to note that the valency and the oxidation number of an atom are not the same terms as the valency of an element is a fixed quantity while the oxidation state varies from molecule to molecule depending upon the type of atom it is bonded with. Moreover, the valency of an atom is a pure number whereas the oxidation state may have a positive, negative or zero value.