Question

Give some examples of non-symbiotic bacteria which fix nitrogen.

Answer 1

Nitrogen fixation is the process of converting atmospheric nitrogen to a form of nitrogen such as ammonia through natural or artificial methods. In nature, microbes extract the majority of nitrogen from the atmosphere and convert it to ammonia, nitrites, and nitrates, which plants may utilise. Nitrogen fixing organisms are known as diazotrophs.

Complete answer:
To solve this question one should know about nitrogen fixing bacteria.
A specialised subset of prokaryotes performs biological nitrogen fixation (BNF), which was identified by Beijerinck in $1901$ (Beijerinck $1901$). The enzyme nitrogenase catalyses the conversion of atmospheric nitrogen (${N_2}$) to ammonia in these organisms ($N{H_3}$).
Nitrogen fixing bacteria can be classified as symbiotic nitrogen fixing bacteria and non-symbiotic nitrogen fixing bacteria.
Symbiotic nitrogen fixing bacteria usually fix nitrogen in a symbiotic association with the host plant like Rhizobium in the root nodules of leguminous plants.
Non-symbiotic or free living nitrogen fixing bacteria fix nitrogen without the host living freely and convert atmospheric nitrogen to nitrites and nitrates.
Some examples of non-symbiotic nitrogen fixing bacteria are as follows –
Azotobacter
Bacillus
Clostridium
Klebsiella

Note:
Nitrogen is a necessary ingredient for plant growth and development, but it is in short supply in its most common form, atmospheric nitrogen. Plants, on the other hand, rely on compounded, or fixed, nitrogen sources like ammonia and nitrate. Much of this nitrogen is supplied to cropping systems in the form of nitrogen fertilisers manufactured in factories. Biological nitrogen fixation, on the other hand, provides plants with a natural source of nitrogen. It's an important part of many aquatic and terrestrial ecosystems all around the world.