In which of the following compounds can the $X^{-}$ atom be most easily substituted by a stronger nucleophile?

The reaction of toluene with chlorine in the presence of ferric chloride $(FeCl_3)$ gives predominantly:

Why do aryl halides undergo electrophilic substitution reactions at $o-$ and $p-$positions? Why are they less reactive than benzene?

Aryl halides are extremely less reactive towards nucleophilic substitution. Predict and explain the order of reactivity of the following compounds towards nucleophilic substitution:
$(I)$ $p$-nitrochlorobenzene
$(II)$ $2,4$-dinitrochlorobenzene
$(III)$ $2,4,6$-trinitrochlorobenzene

Which of the following compounds has a dipole moment approximately equal to that of chlorobenzene?

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