The correct answer is C. Ethine.
An unsaturated hydrocarbon is a hydrocarbon that has double or triple bonds between carbon atoms. Ethine, also known as acetylene, is the simplest unsaturated hydrocarbon. It has the chemical formula $C_2H_2$ and is a colorless, flammable gas. Ethine is used in the production of plastics, synthetic fibers, and other chemicals.
Butane, pentane, and propane are all saturated hydrocarbons. They have no double or triple bonds between carbon atoms. Saturated hydrocarbons are more stable than unsaturated hydrocarbons. They are also less reactive.
Saturated hydrocarbons are found in petroleum and natural gas. They are used as fuels in cars, trucks, and other vehicles. They are also used to make plastics, synthetic fibers, and other chemicals.