What is the oxidation number of $C$ in $C_3O_2$?

The oxidation number of oxygen in an $O_2$ molecule is:

$3 \ mole$ of $N_2H_4$ loses $30 \ mole$ of electrons to form a new compound. Calculate the oxidation state of $N$ in the new compound,assuming the oxidation state of $H$ remains unchanged.

Sulphur in $+3$ oxidation state is present in

What is the oxidation number of $Cl$ in $HOClO_2$?

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