State Huckel's rule.

Name three heterocyclic compounds which are aromatic in nature.

Will cyclo-octatetraene show aromatic character?

Cyclobutadiene is not aromatic. Explain. 

55.

what are annulenes? Give one example. 

Which of the following exhibits aromaticity:
(i) Cyclo - octatetraene  (ii) Cyclopentadiene   (iii) Tropylium cation?

Give two examples of ions which are non-aromatic. Why don't they exhibit aromaticity?

Is benzene same as 1, 3, 5-cyclohexatriene?

What is the role of catalyst in electrophilic substitution reactions?

Name the catalysts used in electrophilic aromatic substitution reactions.