x=+3.
The oxidation state of P atom in phosphinic acid H3PO2 is:
3+x−4=0
x=+1.
The oxidation state of P atom in pyrophosphorus acid H4P2O5 is:
4+x−10=0
x=+3.
The oxidation state of P atom in orthophosphoric acid H3PO4 is:
3+x−8=0
x=+5.
Hence, option B is correct.