Consider the reactions:

$\text{X}$ must be Ethanol (${\text{C}}_2{\text{H}}_6\text{O}$) because catalytic dehydrogenation with $\text{Cu}$ at $573\text{K}$ gives Ethanal ($\text{A}$).$\text{A}$ (Ethanal, ${\text{CH}}_3\text{CHO}$) gives a positive silver mirror test (it's an aldehyde).Ethanal reacts with semicarbazide to form Ethanal semicarbazone ($\text{Z}$).Ethanal undergoes aldol condensation in dilute alkali followed by heating to form But-2-enal ($\text{Y}$).