Conversion of $NH_{3} \rightarrow NO_{2}^{-} \rightarrow NO_{3}^{-}$ is called:

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

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?

Which of the following diagrams correctly depicts the $N_{2}$-cycle?

The concentration of nitrogen in the atmosphere remains constant due to:

Identify $X$ and $Y$ in the given nitrogen cycle chart.