Final answer:
In the question, the correct number of pi electrons for benzene is 6, for the cyclopentadienyl anion is 6, for pyrrole is 8, and for furan is also 6. Pi electrons are those involved in pi bonds, and in aromatic compounds, they are delocalized around the ring structure.
Step-by-step explanation:
The question asks for the number of pi electrons in different ring structures. Pi electrons are the electrons in pi bonds, which are found in molecules with double or triple bonds and arise from the sideways overlap of p-orbitals. In aromatic compounds such as benzene, pi electrons are delocalized around the ring structure, contributing to the molecule's stability.
For benzene, a cyclic compound with a hexagonal ring and alternating single and double bonds, there are 6 pi electrons. These electrons are delocalized over the six carbon atoms, and the stability of benzene is represented by a ring or circle in the hexagon's center. This indicates that the double bonds are not localized but are spread out or delocalized throughout the entire ring, which is a defining characteristic of aromatic compounds. The cyclopentadienyl anion, with one negative charge, also has 6 pi electrons due to the extra electron provided by the anion. Pyrrole, with a five-membered ring containing one nitrogen atom, has a total of 8 pi electrons, as the nitrogen atom contributes a pair of electrons to the pi system. Furan, with a five-membered ring with one oxygen atom, also has 6 pi electrons because the oxygen atom has two lone pairs of electrons, but only one of these pairs contributes to the aromatic pi