In the following reaction sequence, the compound $\mathrm{C}$ is
$\mathrm{Al}+{\mathrm{N}}_2\stackrel{\Delta }{⟶}\left(\mathrm{A}\right)\stackrel{{\mathrm{H}}_2\mathrm{O}}{⟶}\mathrm{B}\left(\mathrm{ppt}\right)+\mathrm{C}\left(\mathrm{g}\right)$

Aluminium in form of powder react with nitrogen to produce aluminium nitride this reaction takes place at a temperature of $1073\mathrm{K}-1473\mathrm{K}$. It is shown below:

$\begin{array}{ccccc}2\mathrm{Al}& +& {\mathrm{N}}_2& \to & 2\mathrm{AlN}\\ & & & & \left(\mathrm{A}\right)\end{array}$

Aluminium Nitride $\left(\mathrm{AlN}\right)$ has very high thermal conductivity and excellent electrical insulation properties exhibits wide applications, when it reacts with water it forms the aluminium hydroxide and ammonia gas i.e.

$\begin{array}{ccccc}2\mathrm{AlN}& \stackrel{{\mathrm{H}}_2\mathrm{O}}{\to }& \mathrm{Al}{\left(\mathrm{OH}\right)}_3 \left(\mathrm{ppt}. \downarrow \right)& +& {\mathrm{NH}}_3 \left(\mathrm{g}\right)\\ & & \left(\mathrm{B}\right)& & \left(\mathrm{C}\right)\end{array}$

Hence, the product $\mathrm{C}$ is Ammonia $\left({\mathrm{NH}}_3\right)$ gas.