What is the oxidation state of iodine in $I_2Cl_6$?

In chromite ore,the oxidation number of iron and chromium 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.)

Oxidation number of oxygen in potassium superoxide $(KO_2)$ is

What is the oxidation number of $S$ in $H_2SO_4$?

What is the oxidation number of $N$ in $NH_2-NH_2$?