Answer:
The correct option is D. It is carbon dioxide released by respiration.
Explanation:
The process by which ATP is abundantly formed in organisms is termed as cellular respiration. Cellular respiration can be described as a process in which carbon dioxide and water are produced from glucose and oxygen. ATP molecules are synthesized by this process which are used for cellular activities.
Hence, the substance X in the investigation shows carbon dioxide which was produced when the yeast cells began to respire. Yeast cells can respire either in the presence of oxygen or without oxygen.