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Answer» `IV gt I gt III gt II`
`III gt I gt IV gt II`
`II gt I gt III gt IV`
`I gt III gt II gt IV` Solution :Piperidine (I) is a `2^(@)` alphatic amine. As such it is most basic with `K_(b)=2xx10^(-3)`. Pyrrole (IV) with `K_(b)=2.5xx10^(-14)` is least basic of all the four. In pyrrole, the N is `sp^(3)` hybridised and the lone pair on N is involved in `pi`-electron cloud. Thus is due to non availability of lone pair on N for sharing with acids, it is least basic of the four. In pyridine (II) N is `sp^(2)` hybridised and the UNPAIRED electron in the unhybridised p-orbital is involved in `pi`-electron cloud. As such the lone pair on N PRESENT in `sp^(2)`-hybridised orbital is available for sharing with acids. Thus it is more basic than pyrrole. The value of `K_(b)` for pyridine is `2.3 xx 10^(-9)`. In (III) the lone pair on N is LESS readily available because of electronegative O atom present in the skeleton RING. Thus (III) is less basic than (I).
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