What is meaning of oxidation in easy words i cannot understand from this picture i need meaning of oxidation and meaning of biological nitrogen fixation in easy words i need plz ans meritnation experts

Dear student,
Please find below the answer:

In simple words, oxidation is just the addition of oxygen to another molecule.

When the atmospheric nitrogen is converted to ammonia by some specialized group of prokaryotes like cyanobacteria, Azotobacter (free-living soil bacteria), Rhizobium (symbiotic bacteria) etc. the process is known as biological nitrogen fixation. This process is useful to fulfil the necessity of nitrogen for agriculture.  

Hope this clears your doubt.
Regards.