Correct Option: D

Nitrogen fixation is a process by which nitrogen in the Earth’s atmosphere is converted into ammonia (NH₃) or other molecules available to living organisms. Atmospheric nitrogen or molecular dinitrogen (N₂) is relatively inert: it does not easily react with other chemicals to form new compounds. The fixation process frees nitrogen atoms from their triply bonded diatomic form, NºN, to be used by plants as nutrients. The conversion of organic nitrogen to proteins is achieved in Nitrogen cycle.