The oxidation number of carbon in $CH_2O$ is

The correct set of oxidation numbers of $N$ in $NH_4NO_2$ is

What is the oxidation number of $Cl$ in $CaOCl_2$?

In which among the following compounds,the oxidation number of nitrogen is $ +5 $?

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

Fill in the blanks:
$(1)$ During the reaction $CN^{-} \to CNO^{-}$,......... is added.
$(2)$ The maximum positive oxidation number for any chalcogen compound may be ......... .