The oxidation number of $H$ in $KH$,$MgH_2$,and $NaOH$ are respectively

Calculate the oxidation number of nitrogen and chlorine in $NOClO_4$.

In the following reaction,assign the oxidation state of the underlined atom for the product of complete hydrolysis at $R.T.$:
$H\underline{N}O_4 + H_2O \longrightarrow HNO_3 + H_2O_2$

Oxidation number of $As$ atoms in $H_3AsO_4$ is

In acidic medium,$H_2O_2$ changes $Cr_2O_7^{2-}$ to $CrO_5$ which has two $(-O-O-)$ bonds. Oxidation state of $Cr$ in $CrO_5$ is

What is the oxidation state of oxygen in $O_2^{2-}$ ion?