Give one methods of preparation of benzene diazonium chloride. Write its synthetic applications for preparation of (a) chlorobenzene (b) phenol (c) benzene (d) iodobenzene.

Explanation

Preparation Aniline reacts with nitrous acid produced in situ from `NaNO_(2)` and HCl at 0 - 5°C to give benzene diazonium chloride. This reaction is known as diazotisation reaction.
`NaNO_(2) + HCl to HNO_(2) + NaCl`
`underset("Aniline")(C_(6)H_(5)) - NH_(2) + HNO_(2) + HCl overset(0-5^(@) C) to underset("Benzene diazonium, chloride")(C_(6)H_(5)- N_(2)^(+) Cl^(-) + 2H_(2)O)`