The gas used in artificial ripening of green fruits is

Fruit ripening — softening, the breakdown of starch into sugar, and the change in colour as chlorophyll degrades — is triggered inside the fruit by the plant hormone ethylene (C2H4). An artificial ripening agent works by mimicking ethylene's action on this same pathway.

Producing pure ethylene gas is possible via controlled, enclosed ripening chambers — the FSSAI-approved method — but this requires dedicated ethylene-generation infrastructure. Calcium carbide (CaC2), by contrast, is cheap and needs no such setup, so fruit traders have long used it as a low-cost shortcut ripening agent instead. Calcium carbide reacts with the moisture naturally present on a fruit's surface to release acetylene (C2H2) gas, which chemically mimics ethylene and switches on the same ripening enzymes — producing rapid, though often uneven and unsafe, ripening.

• Ethane is a stable, unreactive saturated hydrocarbon; it does not interact with the ripening-enzyme pathway and plays no role in fruit ripening.

• Hydrogen gas has no involvement in the biochemical changes of fruit ripening.

• Nitrogen is used the opposite way — in controlled-atmosphere storage it displaces oxygen to slow ripening and extend shelf life, not to induce it.

Acetylene is therefore the gas among the options that is used to artificially ripen green fruits — though this calcium-carbide-based method is now banned by food-safety regulators (FSSAI) due to toxic arsenic and phosphorus residues, with regulated ethephon-based ethylene-generation in enclosed ripening chambers being the officially approved safe alternative.