Which compound posses highest dipole moment ?

Answer: DSolution: Polycycilic systems : Huckel's $\left(4n+2\right)$n rule applies to monocyclic system. The rule, however , is not necessarily succesful for polycyclic conjugated system,

The (4n+2) rule should be applied to the peripheral (conjugated ) $\pi$ electrons . The five-membered ring has five and the seven-membered ring has seven $\pi$ electrons (two $\pi$ electrons are common to both rings ) . If one $\pi$ electron is transferred from the seven -to the five. ring , each will now have a closed shell of six $\pi$ electrons (cf. naphtalene) . In this condition, the molecule will have a dipolar structure, and this has been shwon to be the case from dipole -moment measurements. Azulene also behaves chemically as an aromatic compound.