Determine the oxidation state of each element in $CO{H}_2$ (assume typical oxidation-state rules for covalent compounds).

What is the oxidation number of Fe in Fe_2O_3?

What is the oxidation number of aluminum in Al2O3?

What is the oxidation state of copper (Cu) in Cu_2O?

In which reaction does the oxidation number of oxygen increase (i.e., becomes less negative or more positive)?

In the compound $N_2{H}_4{O}_2$ (often written as $N_2{H}_4{O}_2$), nitrogen occurs in two different ions: $N_1^{+}$ in $N_1{H}_4$ and $N_1^{-}$ in $N_1{O}_2$. What are the oxidation numbers of nitrogen in these two ions (in the order $N_1{H}_4$ then $N_1{O}_2$)?

What is the average oxidation number of sulfur in sodium thiosulfate, $N_a{2}_{}{S}_2{O}_3$?

Which compound contains an atom with the highest oxidation number?

When determining oxidation numbers, how can you find the oxidation number of a monatomic ion (an ion made of a single element)?