Question

Calculate the oxidation number of the underlined elements.
a. $\underset{–}{P}{H}_3$ b. $\underset{–}{S}{O}_2$ c. $H\underset{–}{N}{O}_3$ d. $H_3\underset{–}{P}{O}_4$

• A. a. $-3$; b. $+4$; c. $+5$; d. $+5$
• B. a. $-3$; b. $+2$; c. $+5$; d. $+5$
• C. a. $-3$; b. $+4$; c. $+5$; d. $+4$
• D. None of these

Answer 1

The correct option is A a. $-3$; b. $+4$; c. $+5$; d. $+5$

a) Let $x$ be the oxidation number of P in phosphine $P{H}_3$.
Since, the overall charge on the complex is $0$, the sum of oxidation states of all elements in it should be equal to $0$.
$x+3(+1)=0$
$x=+3$.
Similarly,
b) Let $x$ be the oxidation number of S in sulphur dioxide $S{O}_2$.
$x+2(-2)=0$
$x=+4$.
c) Let $x$ be the oxidation number of N in nitric acid $HN{O}_3$.
$1+x+3(-2)=0$
$x=+5$.
Let $x$ be the oxidation number of P in phosphoric acid $H_{3}P{O}_4$.
$3(+1)+x+4(+1)=0$
$x=+5$.