Final answer:
Air is primarily composed of nitrogen (78.6 percent), oxygen (20.9 percent), water vapor (0.5 percent), and carbon dioxide (0.04 percent).
Step-by-step explanation:
Air is primarily composed of nitrogen (N2; 78.6 percent), oxygen (O2; 20.9 percent), water vapor (H2O; 0.5 percent), and carbon dioxide (CO2; 0.04 percent).
The atmospheric composition can also vary with the presence of trace amounts of other gases and dust particles suspended in the air.