why ethylene can accelerate ripening of fruit?

Ethylene (IUPAC name: ethene) is an organic compound, a hydrocarbon with the formula C₂H₄ or H₂C=CH₂. It is a colorless flammable gas with a faint "sweet and musky" odor when pure.^] It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds), and the simplest unsaturated hydrocarbon after acetylene (C₂H₂).

Ethylene is a plant hormone first in the form of gas. If the fruit is ripe oranges combined with bananas, ripe bananas are faster because oranges emit ethylene gas. The discovery of this hormone in plants first described by R. Gane in 1934.

Ethylene is a plant and cause more rapid maturation in many fruits, including bananas. Ethylene formation requires O2 and is inhibited by CO2. All parts of the plant can produce ethylene gas angiosperms. Formation mainly occurs in roots, shoot apical meristem, mode, fall flowers and ripe fruit.

In fruit ripening, ethylene working to solve the chlorophyll in young fruit, so the fruit has only xantofil and carotene. Thus, the color becomes orange or red fruit.
In other applications, ethylene is used as an anesthetic (anesthetic).

Calcium Carbide is NOT safe for ripening. Calcium Carbide is used in some countries as source of acetylene gas, which is an artificial ripening agent. However, acetylene is not nearly as effective for ripening as is ethylene, and acetylene is not a natural plant hormone like ethylene. Also, calcium carbide may contain traces of arsenic and phosphorus, both highly toxic to humans, and the use of this chemical for ripening is illegal in most countries.