The oxidation states of P in H4P2O7, H4P2O5 and H4P2O6, respectively, are:

Step 1 — Oxidation state of P in $\mathrm{H_4P_2O_7}$ (pyrophosphoric acid): $4(+1) + 2x + 7(-2) = 0$ $4 + 2x - 14 = 0 \Rightarrow 2x = 10 \Rightarrow x = +5$

Step 2 — Oxidation state of P in $\mathrm{H_4P_2O_5}$ (hypodiphosphorous acid / pyrophosphorous acid): $4(+1) + 2x + 5(-2) = 0$ $4 + 2x - 10 = 0 \Rightarrow 2x = 6 \Rightarrow x = +3$

Step 3 — Oxidation state of P in $\mathrm{H_4P_2O_6}$ (hypophosphoric acid): $4(+1) + 2x + 6(-2) = 0$ $4 + 2x - 12 = 0 \Rightarrow 2x = 8 \Rightarrow x = +4$

Summary:

| Compound | Oxidation state of P | |---|---| | $\mathrm{H_4P_2O_7}$ | $+5$ | | $\mathrm{H_4P_2O_5}$ | $+3$ | | $\mathrm{H_4P_2O_6}$ | $+4$ |

Answer: Option (3) — 5, 3 and 4