What is nitrogen fixation? Why do plants need to fix nitrogen?

(N/A) Nitrogen fixation is the process of converting atmospheric nitrogen $(N_2)$ into usable forms like ammonia $(NH_3)$ or oxides of nitrogen $(NO_x)$.
Plants require nitrogen to synthesize essential biological molecules such as proteins,nucleic acids ($DNA$ and $RNA$),and chlorophyll.
Although nitrogen is abundant in the atmosphere,plants cannot absorb it directly in its gaseous form $(N_2)$ because the triple covalent bond between nitrogen atoms is extremely stable and difficult to break. Therefore,they rely on nitrogen fixation to convert it into a form that can be assimilated by their roots.