Question

Find the oxidation number of elements in each case :

$P$ in $H_{3}P{O}_4,H_{3}P{O}_3,HP{O}_3,P_2{O}_5$ and $P{H}_3$.

• A. $+5,+3,+5,+5,-3$
• B. $+4,+2,+3,+5,-2$
• C. $+5,+3,+4,+5,-3$
• D. None of the above

Answer 1

Answer: (A)

$+5,+3,+5,+5,-3$

The oxidation numbers of P in $H_{3}P{O}_4,H_{3}P{O}_3,HP{O}_3,P_2{O}_5$ are $+5,+3,+5,+5,3$ respectively.
Let X be the oxidation number of P in $H_{3}P{O}_4$.
$3+X+4(-2)=0$
$X=+5$
Let X be the oxidation number of P in $H_{3}P{O}_3$
$3+X+3(-2)$
$X=+3$
Let X be the oxidation number of P in $HP{O}_3$
$1+X+3(-2)$
$X=+5$
Let X be the oxidation number of P in $P_2{O}_5$
$2X+5(-2)=0$
$X=+5$
Let X be the oxidation number of P in $P{H}_3$
$X+3=0$
$X=-3$