Key Idea Oxidation state of H is +1 and that of O is -2. Let the oxidation state of P in the given compounds is x. In H4P2O5, (+1)×4+2×x+(−2)×54+2x−102x∴x=0=0=6=+3 In H4P2O6,(+1)×4+2×x+(−2)×6=04+2x−12=02x=8∴x=+4 In H4P2O7 (+1)×4+2×x+(−2)×74+2x−142xx=0=0=10=+5 Thus, the oxidation states of P in H4P2O5, H4P2O6 and H4P2O7 are +3,+4 and +5 respectively.