In Nitrogen fixation $N_2\qquad\underrightarrow {Nitrogenase}\qquad x \rightarrow NO_2^-\qquad\underrightarrow{\text{In soil}}\qquad y$.The y in the equation is

Question

$\begin{array}{1 1}(a)\;NO_3\\(b)\;NO_2\\(c)\;NO_3^-\\(d)\;NO_4^-\end{array}$