(i) Aniline does not undergo Friedel craft's reactions because
the reagent (the Lewis acid which is used as a catalyst in friedel crafts
reaction), being electron deficient acts as a Lewis base. and attacks on the
lone pair of nitrogen present in aniline to form an insoluble complex which
precipitates out and the reaction does not proceed.
(ii) With increase in alkyl group, the +I effect will increase which will increase the ease of donation of lone pair electron. But in water one other factor is controlling the strength of basicity. Amine will accept a proton and form cation. This cation will be stabilised in water by salvation. Better the salvation by hydrogen bonding, higher will be the basic strength.(refer image)
Thus with increase in methyl group, hydrogen bonding and stabilisation by salvation decreases. The net effect is when we move from secondary to tertiary amine basic strength
(iii) In a tertiary amine there aren't any hydrogen atoms attached directly to the nitrogen. That means that hydrogen bonding between tertiary amine molecules is impossible. That's why the boiling point is much lower. The small amines of all types are very soluble in water.