The correct answer is Ethylene. Green fruits are ripened by ethylene gas. Ethylene is a hydrocarbon that has the formula C ?H? or H?C=CH?. It is a colourless flammable gas with a faint sweet and musky odour when pure. It is the simplest alkene. Ethylene is widely used in the chemical industry, and its worldwide production exceeds that of any other organic compound. Calcium carbide is also used in some countries for artificially ripening fruits. When calcium carbide comes in contact with moisture, it produces acetylene gas, which is similar in its effects to the natural ripening agent, ethylene. The life of fruits can be divided into three phases: fruit set, fruit development, and fruit ripening. Fruit ripening is the initiation of fruit senescence which is a genetically programmed highly coordinated process of organ transformation from unripe to the ripe stage to yield an attractive edible fruit. The ripening process of Banana:Additional InformationGasDetailsAcetyleneAcetylene (systematic name: ethyne) is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. This colourless gas (lower hydrocarbons are generally gaseous in nature) is widely used as a fuel and a chemical building block. HydrogenHydrogen is the chemical element with the symbol H and atomic number 1. With a standard atomic weight of 1. 008, hydrogen is the lightest element in the periodic table. Hydrogen is the most abundant chemical substance in the universe, constituting roughly 75% of all baryonic mass. Carbon DioxideCarbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. It is often referred to by its formula CO2. It is present in the Earth's atmosphere at a low concentration and acts as a greenhouse gas. In its solid-state, it is called dry ice. It is a major component of the carbon cycle.