Question

What are the oxidation states of phosphorus in the following compounds?
$H_{3}P{O}_2,H_{3}P{O}_4,M{g}_2{P}_2{O}_7,P{H}_3,HP{O}_3$

• A. $+1,+3,+3,+3,+5$
• B. $+3,+3,+5,+5,+5$
• C. $+1,+2,+3,+5,+5$
• D. $+1,+5,+5,-3,+5$

Answer 1

The correct option is D $+1,+5,+5,-3,+5$

Let the oxidation number of phosphorous be $x$.

Oxidation number of $H=+1$, $Mg=+2$ and of $O=-2$.

1. $H_{3}P{O}_2$: $3\times 1+x+2\times (-2)=0$

$3+x-4=0$ or $x=+1$

2. $H_{3}P{O}_4$: $3\times 1+x+4\times (-2)=0$

$3+x-8=0$ or $x=+5$

3. $M{g}_2{P}_2{O}_7$: $2\times 2+2x+7\times (-2)=0$

$4+2x-14=0$ or $x=+5$

4. $P{H}_3$: $x+3\times 1=0$

$x=-3$

5. $HP{O}_3$: $1+x+3\times (-2)=0$

$1+x-6=0$ or $x=+5$

Thus the oxidation states of phosphorus in: $H_{3}P{O}_2,H_{3}P{O}_4,M{g}_2{P}_2{O}_7,P{H}_3,HP{O}_3$ is +1,+5,+5,-3,+5, respectively.