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Bananas are most likely to brown when stored in a refrigerator due to the physiological responses of the fruit to cold temperatures. While bananas can be stored at room temperature to ripen properly, refrigeration disrupts their natural ripening process. The cold environment causes the production of ethylene gas, which bananas release as they ripen, to slow down dramatically. However, the skin of bananas contains enzymes that can be adversely affected by cold temperatures, leading to browning or darkening. This browning is a result of the enzymatic reaction that takes place when the fruit is exposed to air after the cell structure is altered by cold.

In contrast, apples, green peppers, and cucumbers are less affected by cold storage; apples can be stored in cool conditions without significant browning, and green peppers and cucumbers do not undergo similar enzymatic browning processes as readily as bananas do. They can still last long in refrigeration without the drastic color change seen with bananas. Thus, the unique response of bananas to refrigeration, leading to browning, makes it the correct response.