Humans primarily breathe in oxygen (O2), which is essential for cellular respiration. This gas is vital for producing energy in our cells. Air consists of roughly 21% oxygen, and it is delivered to the body through the respiratory system when we inhale. Oxygen is crucial for sustaining life, supporting metabolic processes, and enabling the functioning of various organs. Additionally, the process of respiration involves inhaling oxygen and exhaling carbon dioxide (CO2), a waste product generated by the body. Adequate oxygen levels are key for overall health and well-being.