Question

The oxidation number of underlined element in the following compound is :
$\underset{–}{Zn}O{{}_2}^{2-}$

Answer 1

Let $x$ be the oxidation number of $Zn$ in $Zn{O}_2^{2-}$.
Since, the overall charge on the complex is $-2$, the sum of oxidation states of all elements in it should be equal to $-2$.
Therefore, $x+2(-2)=-2$
or, $x=+2$
Hence, the oxidation number of $Zn$ in $Zn{O}_2^{2-}$ is $+2$.