What is the oxidation number of carbon in methanal?

The oxidation state of iodine in $I_3^{-}$ is:

The oxidation number of carbon in $CH_2Cl_2$ is .........

Oxidation number of $Mn$ in $K_2MnO_4$ and in $KMnO_4$ are respectively

The oxidation state of the oxygen atom in potassium superoxide is:

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.)