The basicity of an amine depends on the ability of its nitrogen atom to donate lone pair of electrons in an acid-base reaction. Resonance, inductive effect and steric hindrance etc. plays a very important role in deciding the basicity of compound.

Among the given compounds, (III) is most basic due to the presence of electron donating methyl group which increases the electron density on nitrogen. Compound (IV) is less basic than (III). Hybridisation of nitrogen atom in aniline (I) and pyrrole (II) is sp³ and sp² , respectively, therefore, (I) is more basic than (II). Thus, the correct order of basicity is