An orange solid (X) on heating, gives a colourless gas (Y) and a only green residue (Z). Gas (Y) on treatment with Mg, produces a white solid substance

Nitrogen gas is produced when ammonium dichromate is heated, and magnesium treatment with the nitrogen gas results in the production of magnesium nitride.

$\begin{array}{l}{\left({\mathrm{NH}}_4\right)}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\to {\mathrm{N}}_2+{\mathrm{Cr}}_2{\mathrm{O}}_3+4{\mathrm{H}}_2\mathrm{O}\\ 3\mathrm{Mg}+{\mathrm{N}}_2\to {\mathrm{Mg}}_3{\mathrm{N}}_2\end{array}$

Orange solid is ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$,Colourless gas is ${\mathrm{N}}_2$and Green residue is ${\mathrm{Cr}}_2{\mathrm{O}}_3$.