Question

What are the oxidation number of the underlined elements in each of the following and how do you rationalise your results?

$K{\underset{–}{I}}_3$

Answer 1

Let X be the oxidation number of I in $K{I}_3$
$+1+3X=0$
$X=-\frac{1}{3}$
But the oxidation number cannot be fractional.

$K{I}_3$ exists as $K^{+}[I-I\leftarrow I{]}^{-}$. A coordinate bond is formed between $I_2$ molecule and $I^{-}$ ion.

The oxidation number of two I atoms in $I_2$ molecule is 0 and that of $I^{-}$ ion is -1.