O-2, also known as oxygen, is a colorless, odorless gas that is essential for life on Earth. It makes up about 21% of the atmosphere and is crucial for the process of respiration in animals and humans. Plants produce oxygen through photosynthesis, converting carbon dioxide and sunlight into energy. In addition to its biological importance, O-2 is used in various industrial applications, including metal cutting and welding. It is also a key component in medical treatments, such as oxygen therapy for patients with respiratory issues. Understanding O-2 is vital for both environmental science and health care.