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

Reaction carried out by $N_{2}$ metabolising microbes include:
$I.$ $2 NH_{3} + 3 O_{2} \rightarrow 2 NO_{2}^{-} + 2 H^{+} + 2 H_{2} O$
$II.$ $2 NO_{2}^{-} + O_{2} \rightarrow 2 NO_{3}^{-}$
Which of the following statements about these equations is not true?

The limiting factor in the process of nitrification in soil is:

$NO_2^- \rightarrow NO_3^-$
The above mentioned reaction occurs in the presence of .....

$A$: 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.

Describe the Nitrogen Cycle.