The oxidation number of $S$ in $S^{2-}$ is:

What is the oxidation number of the oxygen atom in the $O_2^{2-}$ ion?

What is the order of the oxidation number of $S$ in $SO_3^{2-}$,$S_2O_4^{2-}$,and $S_2O_6^{2-}$?

The oxidation number of an element in a compound is evaluated on the basis of certain rules. Which of the following rules is not correct?
$1$. The oxidation number of hydrogen is always $+1$.
$2$. The algebraic sum of all the oxidation numbers of all elements in a compound is zero.
$3$. An element in the free or the uncombined state bears oxidation number zero.
$4$. In all its compounds,the oxidation number of fluorine is $-1$.

The characteristic oxidation number of atoms in free metals is

The oxidation number of carbon in $CH_2O$ is