Explain how oxides of nitrogen form in car engines and describe their removal by catalytic converters, e.g. (2CO + 2NO ightarrow 2CO_2 + N_2)

Identify redox reactions by changes in oxidation number using: (a) the oxidation number of elements in their uncombined state is zero (b) the oxidation number of a monatomic ion is the same as the charge on the ion (c) the sum of the oxidation numbers in a compound is zero (d) the sum of the oxidation numbers in an ion is equal to the charge on the ion