Which of the following compounds is non-aromatic in nature?

Step-by-step solution

According to Huckel's rule, a planar, fully conjugated cyclic system with (4n+2) electrons is aromatic, while one with 4n electrons is anti-aromatic. Azulene is a fused bicyclic system with 10 electrons ( n=2 ). It is planar and aromatic. Pyrrole is a five-membered heterocycle. The lone pair on the nitrogen atom participates in conjugation, giving 6 electrons ( n=1 ). It is planar and aromatic. Cyclopropenyl cation has 2 electrons ( n=0 ) in a continuous cyclic array of p-orbitals. It is planar and aromatic. Cycloo