
As we can clearly see in the structure,
the number of P−OH bonds is 4.
The oxygen is an electronegative element and will always carry a negative charge. Now, it depends on its surrounding atoms about what charge it carries. In case of a hydroxyl group, the hydrogen carries a +1 charge. So, the opposite charge generated on the oxygen atom along with magnitude will be -1.
In the case of only oxygen atoms, we know that the oxidation number of oxygen is equal to -2. So, the charge generated on the adjacent atom of oxygen will be +2.
Thus, the oxidation state of phosphorus atom will be generated because of:
Oxidation state on phosphorous =[2×(P−OH)+(1×=O)+(1×−O)] oxidation states
Thus, the oxidation state of both the phosphorus atoms will be:
PO.S=2×(+1)+1×(+2)+1×(+1)=+5