A metal $$X$$ on heating in nitrogen gas gives $$Y.$$ $$Y$$ on treatment with $${H_2}O$$  gives a colourless gas which when passed through $$CuS{O_4}$$  solution gives a blue colour. $$Y$$ is

Solution :
\[3Mg+{{N}_{2}}\xrightarrow{\Delta }M{{g}_{3}}{{N}_{2}}\]     \[\xrightarrow{6{{H}_{2}}O}3Hg{{\left( OH \right)}_{2}}+2N{{H}_{3}};\]       \[CuS{{O}_{4}}+4N{{H}_{3}}\to \underset{\text{deep blue colour}}{\mathop{\left[ Cu{{\left( N{{H}_{3}} \right)}_{4}} \right]S{{O}_{4}}}}\,\]