Oxidation number of osmium $(Os)$ in $OsO_4$ is

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

In which of the following does phosphorus have an oxidation state of $+3$?

What are the oxidation states of three $Br$ atoms in $Br_3O_8$ molecule?

One mole of $N_2H_4$ loses $10 \ mol$ of electrons to form a new compound $Y$. Assuming that all nitrogen atoms appear in the new compound,what is the oxidation state of $N$ in $Y$? (There is no change in the oxidation state of hydrogen)

The oxidation state of $Cr$ in $CrO_5$ is