Question

What is the oxidation number of chlorine in $Cl{O}_3^{-}$?

• A. $+5$
• B. $+3$
• C. $+4$
• D. $+2$

Answer 1

The correct option is A $+5$

Let $x$ be the oxidation number of chlorine in $Cl{O}_3^{-}$.
The oxidation number of oxygen is $-2$.
The sum of the oxidation numbers of chlorine and oxygen is $-1$, which is equal to the charge on ion.
Hence, $x+3(-2)=-1$ or, $x=+5$.