Question

the following are the broad classes of organic compounds except:
organic compounds composed of carbon and hydrogen only
compounds containing nitrogen
organic compounds containing oxygen
organic compounds composed of hydrogen only

Explanation:

Organic compounds must contain carbon. The option "organic compounds composed of hydrogen only" has no carbon, so it's not a class of organic compounds. Other options involve carbon (with H, N, or O).

Answer:

D. organic compounds composed of hydrogen only