Final answer:
The two most abundant gases in the atmosphere are nitrogen and oxygen, making up about 78% and 21% of the atmosphere, respectively.
Step-by-step explanation:
The two most abundant gases in the Earth's atmosphere are nitrogen and oxygen. Nitrogen makes up approximately 78% of the atmosphere and plays a critical role in diluting oxygen, which comprises about 21%, to prevent rapid combustion and is essential for aerobic respiration in living organisms. While there are other gases in the atmosphere, such as water vapor and carbon dioxide, they are present in much lower concentrations.