Which of the following gases is essential for human respiration?

Oxygen is essential for human respiration because it plays a crucial role in the process of cellular respiration, which occurs in the body's cells. This process involves the conversion of glucose and oxygen into energy, carbon dioxide, and water. The energy produced is vital for all bodily functions and activities.

When we inhale, oxygen enters the lungs and is transferred to the bloodstream, where it binds to hemoglobin in red blood cells. These oxygen-rich blood cells then circulate throughout the body, delivering oxygen to the cells that need it for metabolism.

Insufficient oxygen levels can lead to hypoxia, which can cause serious health issues, including organ failure and death. In contrast, carbon dioxide, nitrogen, and carbon monoxide, while related to respiratory processes in different ways, do not serve the same crucial function as oxygen in sustaining human life. Carbon dioxide is actually a waste product that is expelled during respiration, nitrogen is inert and does not participate in metabolic processes, and carbon monoxide is a toxic gas that can interfere with oxygen delivery in the body.