The Ullmann reaction is used for the preparation of .......

Which of the following is least reactive towards $S_NAr$?

In which of the following is the chlorine atom least reactive towards nucleophilic substitution?

Chlorination of toluene in the presence of ferric chloride gives........

The compounds $P$,$Q$,and $S$ were separately subjected to nitration using $HNO_3 / H_2SO_4$ mixture. The major product formed in each case respectively,is

What are $Y$ and $Z$ respectively in the following reaction sequence?
Chlorobenzene $\xrightarrow[Conc. H_2SO_4]{HNO_3}$ $X$ (major product) $\xrightarrow{Y}$ $Z$