Hi Amolika,

Find Oxidation no. of P in H₄P₂O₇

Let The oxidation number of P in H₄P₂O₇ is x.

Now follow this no. of first atom x valency of the first atom + no. of second atom x valency of second atom

just like this   

∴ 4(+1) + 2x + 7(-2) = 0
or, x = +5
Thus, the oxidation number of P in H₄P₂O₇ is +5.

Thanks for asking

Good day :)