Question

Oxidation state of phosphorus in pyrophospate ion $\left(P_2{O}_7^{-4}\right)$ is:

• A. $+7$
• B. $+3$
• C. $+8$
• D. $+5$

Answer 1

The correct option is D $+5$

Let $x$ be the oxidation state of phosphorus in pyrophosphate ion $\left(P_2{O}_7^{4-}\right)$.

The oxidation state of oxygen is $-2$. The charge on the ion is $-4$.

Hence, the sum of the oxidation states of phosphorus and oxygen must be $-4$.

$2\left(x\right)+7(-2)=-4$

or, $x=+5$