Final answer:
Oxygen is produced during the light-dependent reactions of photosynthesis, specifically within the electron transport chain of the thylakoid membranes, due to the photolysis of water.
Step-by-step explanation:
Oxygen is produced during the light-dependent reactions of photosynthesis, which take place within the thylakoid membranes of the chloroplasts. Specifically, oxygen is a byproduct of the splitting of water molecules, a process known as photolysis, which occurs during the electron transport chain of these light-dependent reactions. As the electrons are passed from water to the electron transport chain, oxygen is released as a byproduct. Therefore, the correct answer to the question is b) Electron transport chain.
It's important to note that other processes mentioned, such as the Calvin cycle and Krebs cycle, are not directly involved in the production of oxygen. The Calvin cycle, for example, takes place in the stroma and is focused on carbon fixation, producing sugars like Glyceraldehyde-3-Phosphate (G3P). The Krebs cycle, part of cellular respiration, occurs in the mitochondria of cells and does not produce oxygen.