The correct answer is option 3 - Photosynthesis and Oxygen.

Photosynthesis is the process in plants where they use sunlight, carbon dioxide, and water to produce glucose (a type of sugar) and release oxygen as a byproduct. This process occurs in the chloroplasts of plant cells, specifically in the green pigment called chlorophyll.

During photosynthesis, plants convert light energy into chemical energy in the form of glucose. The oxygen produced during photosynthesis is released into the atmosphere and is a vital component for many living organisms, including humans. It is essential for the process of respiration, which occurs in the cells of organisms and involves the breakdown of glucose to release energy for life processes. Oxygen is used in the process of respiration to break down glucose, and in turn, ATP (adenosine triphosphate) is produced, which is the main energy currency of cells.

Therefore, option 3, which states that photosynthesis produces oxygen as a gaseous product, is the correct answer.