What is the oxidation state of oxygen in $OF_2$ and in $KO_2$ respectively?

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

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

The oxidation state of iodine in $H_4IO_6^-$ is

Identify the species in which the central atom has an oxidation state of $+6$.

The equivalent weight of $MnSO_4$ is half of its molecular weight when it is converted into .....