(i) Ammonolysis of alkyl halides leads to the formation of mixture of primary, secondary, tertiary amines and quaternary salts. It is because every time nucleophilic substitution reaction takes place in which amine acts as a nucleophile and form primary amine which further react and form secondary amine, which again react with the alkyl halide to form the tertiary amine, and further leads to the formation of quaternary salt. Thus, ammonolysis reaction forms a mixture of all the four compounds and it will be difficult to get the pure amine.
R−X Alkyl halide ‌

NH3

────▸

−HX

R−NH2‌

R−X

────▸

−HX

R2‌NH‌

R−X

────▸

−HX

‌R3‌N‌

R−X

────▸

‌R4‌

+

N

‌X−
(ii) Aniline does not undergo Friedel-Crafts reaction because aniline act as a strong base which reacts with AlCl3 to form salt. Thus, due to the presence of positive charge on N-atom electrophilic substitution is deactivated in benzene ring.

(iii) Nitration is carried out in an acidic medium. In a strongly acidic medium, aniline is protonated to give anilinium ion (which is meta-directing). For this reason, aniline on nitration gives a substantial amount of m-nitroaniline.