The air composition that makes up about 78% of the atmosphere is primarily?

Nitrogen is the correct answer as it constitutes approximately 78% of Earth's atmosphere. This element is essential for several biological processes, including nitrogen fixation, which is vital for plant growth. It plays a key role in the structure of proteins and nucleic acids, making it significant for life.

In contrast, oxygen makes up about 21% of the atmosphere and is critical for respiration in most living organisms, but it is not the predominant gas. Hydrogen is present in the atmosphere at only trace levels, primarily in the form of hydrogen compounds, and carbon dioxide, while important in the context of greenhouse gases and plant photosynthesis, comprises about 0.04% of the atmosphere. Understanding the predominant gases in the atmosphere helps in comprehending their effects on air quality and environmental conditions.