The oxidation number of $Ba$ in barium peroxide is

Assign the oxidation number to the underlined element in each of the following species:
$1$. $NaH_{2}\underline{P}O_{4}$
$2$. $NaH\underline{S}O_{4}$
$3$. $H_{4}\underline{P_{2}}O_{7}$

Oxidation number of Nitrogen in $NH_4NO_3$ is

What is the oxidation state of $Mn$ in $MnO_4^{-}$?

The correct set of oxidation numbers of $Br$ in $Br_3O_8$ is

Which of the following statements is not correct?