What is the primary function of an oxygen mask in an aircraft?

The primary function of an oxygen mask in an aircraft is to supply supplemental oxygen to prevent hypoxia at high altitudes. At elevated altitudes, the partial pressure of oxygen in the atmosphere decreases, which can lead to insufficient oxygen being available for breathing. This condition, known as hypoxia, can impair cognitive and physical functions, which is particularly dangerous during flight operations. By providing supplemental oxygen through masks, pilots and passengers can maintain adequate oxygen levels, ensuring safety and operational effectiveness in situations where the ambient oxygen concentration is insufficient, such as during cabin depressurization or at cruising altitudes.

The other options, while they may represent other functions or systems in an aircraft, do not accurately reflect the primary purpose of an oxygen mask. Filtering cabin air pollutants relates to air quality control systems, cooling the aircraft is managed by the aircraft's environmental control systems, and assisting in communication is typically handled through radios and intercoms rather than oxygen masks. Thus, focusing on the supply of supplemental oxygen highlights the critical safety role oxygen masks play in aviation.