What defines an unsaturated hydrocarbon?

An unsaturated hydrocarbon is characterized by the presence of double or triple carbon-carbon bonds. In the case of option B, which states it contains double bonds, this is a key feature of unsaturated hydrocarbons, as they are capable of undergoing reactions that saturated hydrocarbons, which only contain single bonds, cannot.

Unsaturated hydrocarbons include alkenes, which possess at least one double bond between carbon atoms, and alkynes, which contain at least one triple bond. The presence of these multiple bonds allows unsaturated hydrocarbons to react with more types of chemicals, making them chemically reactive compared to their saturated counterparts.

The other options focus on single bonds or the presence of only carbon and hydrogen atoms, which do not define an unsaturated hydrocarbon. An unsaturated compound, by nature, must have fewer hydrogen atoms than the saturated counterpart, allowing it to have those double or triple bonds. This reactivity is what distinguishes unsaturated hydrocarbons in organic chemistry.