<Tr> <Td> Alcohol, or ethyl alcohol </Td> <Td> Ethanol </Td> <Td> C H OH </Td> <Td> </Td> <Td> (64 - 17 - 5) </Td> <Td> 1 / C2H6O / c1 - 2 - 3 / h3H, 2H2, 1H3 </Td> </Tr> <P> Often a pure substance needs to be isolated from a mixture, for example from a natural source (where a sample often contains numerous chemical substances) or after a chemical reaction (which often give mixtures of chemical substances). </P>

Which of the following is not one of the five classes of legal chemicals