Oxidation number of nitrogen in $NaNO_2$ is

Oxidation state of nitrogen in nitric oxide is

What is the oxidation number of $Xe$ in $Ba_2XeO_6$?

In which pair of species is the oxidation number of chlorine the same?

What is the change in oxidation number of selenium in the following redox reaction?
$SeO_{3(aq)}^{2-} + Cl_{2(g)} + 2OH^- \longrightarrow SeO_{4(aq)}^{2-} + 2Cl_{(aq)}^- + H_2O$

Oxygen has an oxidation state of $+2$ in which of the following compounds?