What type of gas is commonly used to enhance ripening in fruits?

Ethylene is the correct answer because it is a naturally occurring plant hormone that plays a crucial role in the ripening process of fruits. When fruits are exposed to ethylene gas, it triggers various physiological responses that lead to changes in color, texture, and flavor, ultimately resulting in ripening. This gas facilitates the conversion of starches into sugars, softens the fruit, and alters its aroma, making it more appealing to consumers.

Using ethylene in post-harvest treatments allows for more uniform and controlled ripening, which is particularly important for fruit that is picked before it is fully ripe and needs time to reach its peak quality during transport and storage. This process is widely used in the agricultural industry to ensure that fruits arrive at markets in optimal condition.

In contrast, ethanol, carbon dioxide, and methane do not have the same direct role in fruit ripening as ethylene does. While carbon dioxide can have some influence on the storage environment and can slow down enzymatic reactions that lead to ripening, it does not enhance the ripening process itself. Methane and ethanol do not significantly contribute to the ripening of fruits either, making ethylene the clear choice for this function.