How will you differentiative between
(a) aniline and ethylamine (aromatic and aliphatic amines)?
(b) aniline and benzylamine?
(c )aniline `(1^(@))`, methylaniline `(2^(@))` and dimethylaniline `(3^(@))`?

Explanation

Aniline reacts with nitrosous acid from `NaNO_(2)//HCl ` at 273-278K to form a diazonium salt which gives a scarlet azo dye with `beta-` naphthol in NaOH (Dye test)
Ethylamine reacts with nitrous acid to produce ethyl alcohol and nitrogen gas (seen as bubbles).
`C_(2)H_(5)NH_(2)+ONOH to C_(2)H_(5)OH+N_(2)+H_(2)O`
(b) Aniline give dye test [see (a) part]
Benzylamine reacts with nirtrous acid to form benzyl alcohol and nitrogen gas (ssen as bubbles).
`C_(2)H_(5)CH_(2)NH_(2)+ONOH to C_(6)H_(5)CH_(2)OH+N_(2)+H_(2)O`
(c )Aniline `(1^(2)"Amine")` reacts with nitrous acid to form diazonium salt which gives dye test [see (a) part].
Methyl aniline `(2^(@)"Amine")` form nitrosoamine yellow oily liquid on treatment with nitrous acid, which is stable at room temperature. However on reaction with HCl in ether and alcohol, th nitroso(-NO) group to para-position.

Dimethyl aniline `(3^(@)"Amine"`) forms p-nitroso derviative with nitrous acid which on hydroglysis give p-nitrosophenol and methylamine `(2^(@))`