Question

Which of the following is not a saturated hydrocarbon?
(A) Cyclohexane
(B) Benzene
(C) Butane
(D) Pentane

Answer 1

Hint: Saturated means that the hydrocarbon (molecules containing only hydrogen and carbon) has only single bonds and that the hydrocarbon contains the maximum number of hydrogen atoms for each carbon atom. For example alkanes.

Complete step by step solution:
Unsaturated hydrocarbons are hydrocarbons that have double or triple covalent bonds between adjacent carbon atoms.
Now, the term unsaturated (not saturated) means that more hydrogen atoms may be added to the hydrocarbon to make it saturated (i.e. consisting of all single bonds).
All the hydrocarbons containing “ane” suffix contain a single bond between the carbon atoms whereas those containing “ene”suffix contain double bonds between carbon atoms and those having “yne” suffix contain triple bonds between carbon atoms.
Therefore, among the given options, Benzene is not a saturated hydrocarbon due to the presence of double bonds. It is a molecule which is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Its structure is as shown:


Hence, Option B is correct.

Note: Benzene is a clear, colorless, highly flammable and volatile liquid aromatic hydrocarbon with a gasoline like odor. It is used in many chemical industries to make plastics, resins, nylon and synthetic fibers. It is also used to make some types of lubricants, rubbers, dyes, detergents, drugs and pesticides.