Question

The oxidation number of arsenic atom in $H_{3}As{O}_4$ is:

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

Answer 1

The correct option is D $+5$

Let the oxidation number of $As$ in $H_{3}As{O}_4$ be $x$. The oxidation states of $H$ and $O$ are $+1$ and $-2$ respectively. Since the atom as whole is neutral, following equation holds true:

$3\times (+1)+1\times \left(x\right)+4\times (-2)=0⟹3+x-8=0⟹x=8-3⟹x=5$

Hence, answer is D.