Explain the formation of arenium ion.

The major product obtained in the given reaction is:

The major product of the following reaction is:

Among the following, the reaction that proceeds through an electrophilic substitution, is:

What are the starting materials for the preparation of the following?

In the following reaction sequence the major products $\mathrm{A}$ and $\mathrm{B}$ are :

In the following reactions

$\mathrm{X}$ and $\mathrm{Y}$, respectively, are:

In the reaction scheme shown below, $\mathrm{Q}, \mathrm{R},$ and $\mathrm{S}$ are the major products.

 The correct structure of 

In the following reaction, compound $\mathrm{Q}$ is obtained from compound $\mathrm{P}$ via an ionic intermediate.
 

What is the degree of unsaturation of $\mathrm{Q}$?

In the reaction $\left(\mathrm{X}\right)$ and $\left(\mathrm{Y}\right)$ are respectively.