Describe the reactions of nitration and bromination of phenol.

(N/A) Nitration of phenol:
$(i)$ With dilute $HNO_3$ at low temperature,phenol yields a mixture of $o$-nitrophenol and $p$-nitrophenol.
$(ii)$ With concentrated $HNO_3$,phenol is converted to $2,4,6$-trinitrophenol (picric acid).
$(b)$ Bromination of phenol:
$(i)$ With $Br_2$ in $CS_2$ at $273 \ K$,phenol gives a mixture of $o$-bromophenol and $p$-bromophenol.
$(ii)$ With bromine water $(Br_{2(aq)})$,phenol undergoes polybromination to form $2,4,6$-tribromophenol as a white precipitate.