In which of the following is the lone pair of the nitrogen atom part of the aromatic pi sextet?

Apyridine
Bpiperidine
Ccyclohexylamine
Dpyrrole

Answer: D

In pyrrole the nitrogen is sp2 and its lone pair is in a p orbital, contributing two electrons to the six-electron aromatic sextet. In pyridine the lone pair lies in the plane in an sp2 orbital, and piperidine and cyclohexylamine are non-aromatic.

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