(a) (i) Aniline has higher pKb than methylamine because aniline undergoes resonance and the electrons on N-atom are delocalized in benzene ring. Thus, electrons are less available to donate whereas in methylamine electron density on nitrogen atom is greater than aniline. As a result, the acidic character of methylamine is more than aniline and pKb value is less.
(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) Boiling point of primary amines is higher than that of tertiary amines because tertiary amines do not form hydrogen bond due to absence of H-atoms. So, intermolecular forces between tertiary amines are weaker. On the other hand, in primary amines two hydrogen atoms are attached to electronegative N-atom. It leads to the greater magnitude of H-bonding and hence, larger intermolecular forces.
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(b) (i) The increasing order of basic strength in aqueous solution of following amines is
(CH3)3N<CH3NH2<(CH3)2‌NH
(Due to steric hindrance and +I effect of alkyl groups)
(ii) The benzene sulphonyl chloride (C6H5SO2‌Cl) is called Hinsberg reagent.
● It is an organo-sulphur compound.
● It is used for detection and distinction of primary, secondary and tertiary amine in a given sample.
(iii) Pyridine is used in acylation of amines because it acts as a strong base which helps in removing the side product HCl from the reaction mixture. Therefore, it acts as an acceptor for the acid by-product formed during the reaction.