Final answer:
During periods of darkness, a bean plant produces carbon dioxide (CO2) through the process of cellular respiration.
Step-by-step explanation:
In the process of photosynthesis, plants consume carbon dioxide (CO2) and release oxygen (O2).
During periods of darkness, plants undergo cellular respiration, which is the process of breaking down glucose to release energy. This process produces carbon dioxide as a byproduct.
Therefore, the gas produced during periods of darkness in a bean plant is carbon dioxide (CO2).