AP BIOLOGY

Detailed explanation-1: -By far the largest reservoir of total nitrogen on Earth is the dinitrogen gas (N2) in the atmosphere (Table 4.1).

Detailed explanation-2: -Nitrogen cycles through both the abiotic and biotic parts of the Earth system. The largest reservoir of nitrogen is found in the atmosphere, mostly as nitrogen gas (N2). Nitrogen gas makes up 78% of the air we breathe.

Detailed explanation-3: -So the correct answer is ‘Nitrogen cycle’.

Detailed explanation-4: -So the largest nitrogen reservoir on earth is atmosphere.

Detailed explanation-5: -Air is the major reservoir of nitrogen that constitutes 79% of nitrogen gas (N2).