The condition required for an aromatic ring is that it must contain $... \pi-$ electrons.

Benzene is treated with oleum to produce compound $(X)$,which when further heated with molten sodium hydroxide followed by acidification produces compound $(Y)$. The compound $(Y)$ is treated with zinc metal to produce compound $(Z)$. Identify the structure of compound $(Z)$ from the following options.

Which of the following compounds would exhibit aromatic character?

Give the decreasing order of reactivity for the $ESR$ (Electrophilic Substitution Reaction) for the following compounds:
$(1)$ Benzene
$(2)$ Toluene
$(3)$ Chlorobenzene
$(4)$ Nitrobenzene

Which of the following processes is reversible?

Three fused benzene rings are found in