Question

What will be the oxidation number of $I$ in the $K{I}_3$ ?

• A. $-\frac{1}{3}$
• B. $-\frac{1}{4}$
• C. $+4$
• D. $+3$

Answer 1

The correct option is A $-\frac{1}{3}$

Let the oxidation number of $I$ is a in$K{I}_3$.

$\Rightarrow 1+3\times \left(a\right)=0$
$a=-\frac{1}{3}$.

Alternative way,
$K{I}_3,isKI+I_2$
$\therefore$ $I$ has two oxidation no. -1 and 0 respectively.

However factualy speaking oxidation number of $I$ in $K{I}_3$ is an average of two values - 1 and 0.

$\Rightarrow \text{Average}O.N.=\frac{-1+2\times \left(0\right)}{3}=-\frac{1}{3}.$