Which of the following has delocalised electrons?

The electrophile,$E^{+}$,attacks the benzene ring to generate the intermediate $\sigma$-complex. Which $\sigma$-complex is of lowest energy?

The number of possible aromatic benzenoid isomers for $C_6H_4Cl_2$ are

Identify compound $A$ in the following reaction:
$\text{Benzene} + \text{ozone (excess)}$ $\rightarrow \text{Benzenetrizonide}$ $\xrightarrow{A} \text{glyoxal}$

Which of the following processes is reversible?

The major product '$P$' formed in the given reaction is