Which of the following compounds is unsaturated?

C2H4 (ethene) is an unsaturated hydrocarbon because it contains a carbon-carbon double bond (C=C). A compound is called unsaturated when it has at least one double or triple bond between carbon atoms. C3H8 (propane) is an alkane containing single bonds, making it saturated. C4H10 (butane) is an alkane having only single bonds.