Nitrogen gas (n2) is very abundant in the air, but it cannot be utilized by living things unless

it is transformed from lightning, nitrogen-fixing bacteria, or human intervention

it is the gaseous form needed for reentering the lithosphere left parenthesis n subscript 2 right parenthesis

it goes through denitrification, which makes it left parenthesis n o subscript 3 minus right parenthesis

specialized bacteria converting the nitrogen to nitrite ions left parenthesis n o subscript 2 minus right parenthesis