What percentage of the air is nitrogen?

78%

Explanation:

Air is a mixture of nitrogen 78%, oxygen 21%, argon 0.9%, carbon dioxide 0.04% and other gases. Nitrogen is an element that makes up 78% of the air. It is essential to plants for protein synthesis. Though present in large quantities as free nitrogen gas in the atmosphere, it is taken up by plant roots only in the form of ions, such as nitrates and nitrites. Nitrogen is continually recycled in the ecosystem through biological processes involving bacteria.

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