Question

Find the oxidation number of P in $P_2{O}_7^{4-}$.

Answer 1

Let the oxidation number of P be $x$ .

Oxidation number of oxygen is +2 and overall oxidation state of molecule is -4

In $P_2{O}_7^{4-}$,

$2x+7(-2)=-4$

$P$ $O$

$2x-14=-4$

$2x=14-4$

$x=+5$

Hence the oxidation number of P in $P_2{O}_7^{4-}$ is +5.