The correct answer is option 2 - photolysis of water. During photosynthesis, plants use light energy to convert carbon dioxide and water into glucose (carbohydrate) and oxygen. In the light-dependent reactions of photosynthesis, water molecules are split apart through a process called photolysis. This involves harnessing the energy from sunlight to break the bonds of water molecules, releasing oxygen as a byproduct. The liberated oxygen is then released into the atmosphere, contributing to the oxygen levels in the environment. Option 1 - hydrolysis of carbohydrates, is incorrect because carbohydrates are not hydrolyzed during photosynthesis, but rather synthesized. Option 3 - reduction of CO2, is incorrect because CO2 is not reduced to liberate oxygen, but rather converted into glucose. Option 4 - breakdown of chlorophyll, is incorrect because chlorophyll is responsible for capturing light energy, and its breakdown does not directly result in the liberation of oxygen.