What percentage of atmospheric air is composed of nitrogen?

Atmospheric air is primarily composed of nitrogen, making up approximately 78% of the air we breathe. This high percentage is significant because nitrogen is a vital component that does not actively participate in combustion processes, unlike oxygen, which constitutes about 21% of the atmosphere. Understanding the composition of the air is crucial in fire behavior studies, as it highlights the role of oxygen in supporting combustion while illustrating that the majority of the atmosphere is inert nitrogen. This nitrogen-rich environment is a factor in various fire dynamics, influencing flame behavior and the spread of fire. The other percentages mentioned in the options do not accurately reflect the composition of our atmosphere. For example, 21% corresponds to oxygen, which is essential for combustion, while 50% and 90% are not representative of the actual atmospheric composition.