From the left, the first molecule, the cyclopentadienyl cation, is not aromatic. It only has 4 pi electrons and does not fit the 4n+2 rule. The middle molecule, the cycloheptatrienyl cation (or tropylium cation) is aromatic; it has 6 pi electrons and fits the 4n+2 rule (n=1). The last molecule, azulene, is generally considered to be aromatic. It fits the 4n+2 rule (n=2) and is often referred to as a "nonbenzenoid" aromatic compound. It can also be viewed as a fusion of two other aromatic units, the tropylium cation and the cyclopentadienyl anion.

Molecule 1, the cyclopentadienyl cation, is not aromatic. It only has 4 π electrons and does not fit the $4n+2$ rule.

Molecule 2, the cycloheptatrienyl cation (or tropylium cation), is aromatic; it has 6 π electrons and fits the $4n+2$ rule with $n=1$.

Molecule 3, azulene, is generally considered to be aromatic. It fits the $4n+2$ rule with $n=2$, and is often referred to as a "nonbenzenoid" aromatic compound. It can also be viewed as a fusion of two other aromatic units, the tropylium cation and the cyclopentadienyl anion.