Which of the following is a limiting nutrient for both natural and agricultural ecosystems?

$A-$ 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

$A$: Ammonia is oxidized first to nitrite and then to nitrate by the action of $Nitrosomonas$ and $Nitrobacter$ respectively.
$R$: Nitrite thus formed is absorbed by leaves.

$A$ prokaryote responsible for converting ammonia to nitrites is

Choose the correct pair:

Column-$I$	Column-$II$
$I$. Nitrosomonas	Nitrite to nitrate
$II$. Thiobacillus	Denitrification
$III$. Nostoc	Free-living nitrogen fixer
$IV$. Azotobacter	Anaerobic nitrogen fixer