Which gas is essential for human respiration?

Oxygen is essential for human respiration because it plays a critical role in cellular respiration, the process by which cells produce energy. During respiration, oxygen is utilized by the cells to convert glucose into adenosine triphosphate (ATP), the primary energy carrier in cells. This chemical reaction also produces carbon dioxide as a byproduct, which must then be expelled from the body.

In the human respiratory system, oxygen is inhaled into the lungs, where it diffuses into the bloodstream and is transported to cells throughout the body. Without sufficient oxygen, cells cannot perform their functions effectively, which can lead to serious health consequences, including organ failure and death.

Other gases listed, such as carbon dioxide, nitrogen, and hydrogen, do not play a direct role in the body's energy production processes in the same way. Carbon dioxide is a waste product of respiration that needs to be expelled. Nitrogen, while the most abundant gas in the atmosphere, is inert and does not participate in metabolic processes in the body. Hydrogen, although it is involved in certain biological reactions, is not directly required for respiration. Thus, oxygen is the gas that is crucial for sustaining life through respiration.