The oxidation number of phosphorous in $P{O}_4^{3-},P_4{O}_{10}$ and $P_2{O}_7^{4-}$ is :

The correct option is A $+5$
The oxidation number of phosphorous in $P{O}_4^{3-},P_4{O}_{10}$ and $P_2{O}_7^{4-}$ is +5.
Let X be the oxidation number of P in $P{O}_4^{3-}$.
$X+4(-2)=-3$
$X=+5$
Let X be the oxidation number of P in$P_{4.}{O}_{10}$
$4X+10(-2)=0$
$X=+5$
Let X be the oxidation number of P in$P_2{O}_7^{4-}$.
$2X+7(2-)=-4$
$X=+5$