Convert:
$(i)$ $3-$Methylaniline into $3-$nitrotoluene.
$(ii)$ Aniline into $1,3,5-$tribromobenzene.

(N/A) $(i)$ Conversion of $3-$Methylaniline to $3-$nitrotoluene:
$1.$ $3-$Methylaniline reacts with $NaNO_2$ and $HCl$ at $273-278 \ K$ to form $3-$methylbenzenediazonium chloride.
$2.$ This diazonium salt reacts with $HBF_4$ to form $3-$methylbenzenediazonium tetrafluoroborate.
$3.$ Finally,treatment with $NaNO_2$ in the presence of $Cu$ and heat (Schiemann-like reaction variant) yields $3-$nitrotoluene.
$(ii)$ Conversion of Aniline to $1,3,5-$tribromobenzene:
$1.$ Aniline reacts with $Br_2/H_2O$ to form $2,4,6-$tribromoaniline.
$2.$ $2,4,6-$tribromoaniline is treated with $NaNO_2/HCl$ to form $2,4,6-$tribromobenzenediazonium chloride.
$3.$ Reduction of this diazonium salt with $H_3PO_2$ and $H_2O$ removes the diazonium group,yielding $1,3,5-$tribromobenzene.