Give the correct terminologies for the following processes : conversion of organic nitrogen into ammonia, $N_2$ gas to ammonia and ammonia into nitrates respectively.

The correct option is B Ammonification, nitrogen fixation, nitrification
The organic nitrogen of dead plants and animals (decaying biomass) undergoes decomposition to release ammonia. This process is called ammonification. It is carried out by bacteria such as Bacillus vulgaris.
Nitrogen fixation is the conversion of atmospheric nitrogen into compounds of nitrogen like nitrates and ammonia.
Nitrification is the process of oxidation of ammonia into nitrite by bacteria such as Nitrosomonas and later the nitrite is oxidised to nitrate by bacteria such as Nitrobacter.