Question

The oxidation number of phosphorus in ${{Ba}}{\left( {{{{H}}_2}{{P}}{{{O}}_2}} \right)_2}$ is:
A. $ + 3$
B. $ + 2$
C. $ + 1$
D. $ - 1$

Answer 1

Hint: When an atom gains or loses electrons, it attains a charge which is known as oxidation number. It is also known as oxidation state. It can have positive value or negative value or even zero. Since phosphorus is a non-metal, it has oxidation states $ - 3, + 5$ or $ + 3$. But it may vary depending on the atoms attached.

Complete step by step answer:
Let’s calculate the oxidation state of phosphorus in ${{Ba}}{\left( {{{{H}}_2}{{P}}{{{O}}_2}} \right)_2}$.
The given compound can be splitted as ${{B}}{{{a}}^{2 + }}$ and ${\left( {{{{H}}_2}{{P}}{{{O}}_2}} \right)_2}^ - $. If the compound has a charge, the sum of oxidation states of each atoms is that charge.
i.e. sum of oxidation states of hydrogen, phosphorus and oxygen is equal to $ - 1$. Let the oxidation state of phosphorus be ${{x}}$. We know that the oxidation state of atoms in elementary forms is zero and that of hydrogen is $ + 1$. There are two hydrogen atoms. So the oxidation state will be $ + 2$. Oxidation state of oxygen is $ - 2$.
Now let’s calculate the oxidation state of phosphorus as follows:
$\left( {2 \times + 1} \right) + \left( {{{x}} \times 1} \right) + \left( {2 \times - 2} \right) = - 1$
On simplification we get
$\left( { + 2} \right) + \left( {{x}} \right) + \left( { - 4} \right) = - 1 \Leftrightarrow {{x}} - 2 = - 1 \Leftrightarrow {{x}} = + 1$
So we can tell that the oxidation state of phosphorus is $ + 1$.

Hence the correct option is C.

Additional information:
Phosphorus needs a high amount of energy to gain three electrons to attain octet. So it is not the same as that of nitrogen. Nitrogen can form ${{{M}}^{3 - }}$ because it has a very high electronegativity and it is very small in size.

Note: Phosphorus is an element which lies in the group $15$. It has five valence electrons. Its bonding behavior influences the oxidation number. Thus we can say that the oxidation number ranges from a value of $ - 3$ to $ + 5$. It is purely dependent on the electronic configuration of phosphorus