The process of reducing nitrate to gaseous nitrogen is known as:

$A-$ In nature,lightning and ultraviolet radiation provide enough energy to convert nitrogen to nitrogen oxides.
$R-$ Industrial combustion,forest fires,automobile exhausts,and power-generating stations are also sources of atmospheric nitrogen oxides.

Nitrifying bacteria:

Nitrifying bacteria are those which can convert

Nitrite is converted into nitrate by ........ bacteria.

Nitrifying bacteria........