Proceed backward ; tribromobenzene is produced by boiling compound $Z$ with $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} ; \mathrm{Z}$ in turn 15 obtained by diazotisation of $Y$, so $Y$ and $Z$ should have $-\mathrm{NH}_{2}$ and $-\mathrm{N}_{2} \mathrm{Cl}$ groups respectively, in addition to three Br atoms. Hence $\mathrm{X}$ should be $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}$
