‘X’ decolourilizes ${\mathrm{Br}}_2/{\mathrm{CCl}}_4$ and gives red ppt with ammonical cuprous chloride. ‘X’ is

It should be unsaturated and also must contain acidic Hydrogen atom.

$\therefore \mathrm{CH}\equiv \mathrm{CH}\underset{{\mathrm{CCl}}_4}{\overset{{\mathrm{Br}}_2}{\to }}{\mathrm{CHBr}}_2-{\mathrm{CHBr}}_2$

$\mathrm{CH}\equiv \mathrm{CH}\underset{{\mathrm{NH}}_4\mathrm{OH}}{\overset{{\mathrm{Cu}}_2{\mathrm{Cl}}_2}{\to }}\underset{\mathrm{Red}\mathrm{PPt}}{\mathrm{Cu}-\mathrm{C}\equiv \mathrm{C}-\mathrm{Cu}}\downarrow$