(i) Alcohols are weakly basic in nature so easily in presence of strong acids.
(ii) Due to the presence of +ve charge on the oxygen atom, C-O in protonated alcohols became weak hence easily cleaved by halide ions to form alkyl halides.
(iii) Where as phenols are much weaker bases due to delocalisation of the lone pair of electrons on the oxygen atom due to resonance and so are not easily protonated.
(iv) The C-O bond in phenols has some double bond character; hence not easily cleaved by halide ions to form respective alkyl halides.

(i) In phenol, there is +ve charge on th oxygen atom, therefore it does not undergo protonation easily.

(ii) When phenol, benzene diazonium chloride and NaOH solution are mixed, coupling reaction takes place and the product formed is red dye.

Ethers can undergo nucleophilic substitution reactions with HBr or HI. HI is more reactive I than HBr.

When glycerol is treated with a well cooled mixture of concentrated sulphuric acid and fuming nitric acid, nitroglycerine is formed.

(i) From halo arenes(Dows process):
When Chlorobenzene is hydrolysed with 6-8% NaOH at 300 bar and 633K in a closed vessel, sodium phenoxide is formed which on treatment with dilute HCI gives phenol.

(ii) From benzene sulphonic acid:
Benzene is sulphonated with oleum and the benzene sulphonic acid so formed is heated with molten NaOH at 623K gives sodium phenoxide which on acidification gives phenol.