Number of $\pi$ electrons present in naphthalene is :

The electrophile $NO_2^+$ reacts with which of the following compounds? In which case will $NO_2^+$ attack at the meta position?
$(I)$ $C_6H_5-CCl_3$
$(II)$ $C_6H_5-NO_2$
$(III)$ $C_6H_5-CHO$
$(IV)$ $C_6H_5-O^-$

When benzene is treated with excess of $Cl_2$ in the presence of $FeCl_3$ (or $I_2$ as a carrier),the end product is:

Give examples of Friedel-Crafts alkylation.

The product obtained by the complete nitration of toluene is ......... .

$X$ can be prepared by which of the following reactions,except?