Ethylene; olefiant gas.

a flammable colorless gaseous alkene; obtained from petroleum and natural gas and used in manufacturing many other chemicals; sometimes used as an anesthetic

Or Ethylene simplest member of class of aliphatic organic compounds called alkenes, which contain at least one carbon-carbon double bond. Ethylene is a colourless, slightly sweet-smelling gas of formula H2C=CH2. It is slightly soluble in water and is produced in commercial amounts by cracking and fractional distillation of petroleum and from natural gas.