(i) The order of $pK_b$ will decrease as : (iii) p-Nitroaniline < Aniline < p-Toluidine The availability of l.p. on N of p-nitroaniline is drastically reduced by presence of electron withdrawing $–NO_2$ group on it. In contrast, presence of electron releasing $–CH_3$ group increases the electron density on N atom and improves basicity in p-toluidine. Involvement of l.p. of N in resonance causes aniline to have low basicity. In II, the –Me group through its +I effect improves the electron density on N and therefore its basic strength increases. In III, the $–NH_2$ is farther off from benzene ring and hence l.p. is localized on it and hence the basic strength is highest.(iv) In gas phase, basicity follows the order :In gas phase, the stabilization by solvation is not present and hence basicstrength follows the expected order based on +I effect of alkyl groups.Amines can form hydrogen bonds with water and are therefore soluble init. However, the solubility decreases if the mass of the hydrocarbon partincreases.