Final answer:
Nitrogen is the largest portion of atmospheric gas, making up about 78% of the Earth's atmosphere.
Step-by-step explanation:
The largest portion of atmospheric gas is Nitrogen. In the Earth's atmosphere, nitrogen accounts for approximately 78% of the air by volume, significantly more than oxygen at about 21%, and much more than argon which is roughly 0.93%, or the other gases like sulfur, ozone, and carbon dioxide which occur in even smaller amounts. Among these gases, nitrogen plays a critical role in diluting oxygen and preventing rapid combustion at the Earth's surface, while oxygen is essential for aerobic respiration in living organisms and supports the combustion process.