In $KO_2$,the nature of oxygen species and the oxidation state of oxygen atom are,respectively

What is the oxidation number of sulfur in $Na_2S_4O_6$?

State whether the following statements are True or False:
$(1)$ The oxidation number of nitrogen in ammonium chloride $(NH_4Cl)$ is $(-3)$.
$(2)$ The oxidation number of $C$ in methyl chloride $(CH_3Cl)$ is $(-2)$.
$(3)$ In the following reaction,the oxidation number of $Br$ changes from $0$ to $+5$: $Br_2 \to BrO_3^-$.

The oxidation states of $P$ in $PO_4^{3-}$,$S$ in $SO_4^{2-}$,and $Cr$ in $Cr_2O_7^{2-}$ are respectively:

Oxidation numbers of $P$ in $PO_4^{3-}$,of $S$ in $SO_4^{2-}$ and that of $Cr$ in $Cr_2O_7^{2-}$ are respectively

Which metal in the following compounds is not present in a fractional oxidation state?