Is a banana turning black in a cupboard for a week a chemical reaction?

Yes, a banana turning black in a cupboard for a week is a chemical reaction. This process involves the breakdown of chlorophyll and the production of melanin, leading to the darkening of the peel. Additionally, enzymes and ethylene gas contribute to the ripening process, which accelerates the decay and browning. Overall, the changes in color and texture are the result of various chemical reactions occurring in the fruit.