In the following sequence of reactions,${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Br}\stackrel{\mathrm{KOH}\left(\mathrm{alc}\right)}{\to }\mathrm{X}\stackrel{{\mathrm{Br}}_2}{\to }\mathrm{Y}\stackrel{\mathrm{KOH}( \mathrm{alc} )}{\to }\mathrm{Z},$Z is

In the following sequence of reactions,$$\begin{gathered} {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Br}\stackrel{\mathrm{KOH}\left(\mathrm{alc}\right)}{\to } C{H}_2=C{H}_2 \\ \stackrel{ }{C{H}_2=C{H}_2\stackrel{{\mathrm{Br}}_2}{\to } C{H}_{2}Br-C{H}_{2}Br} \\ {\mathrm{CH}}_2\mathrm{Br}-{\mathrm{CH}}_2\mathrm{Br}\stackrel{\mathrm{KOH}( \mathrm{alc} )}{\to }\mathrm{CH}\equiv \mathrm{CH} \end{gathered}$$Z is