Which of the following is least reactive towards $S_{N}1$ reaction?

The reaction of an aromatic halogen compound with an alkyl halide in the presence of sodium and ether is called:

Assertion : $S_{N}2$ reactions always proceed with inversion of configuration.
Reason : $S_{N}2$ reaction of an optically active aryl halide with an aqueous solution of $KOH$ always gives an alcohol with opposite sign of rotation.

Which of the following reasons support that aryl halides are less reactive than alkyl halides towards nucleophilic substitution reactions?
$a)$ The formation of more stable arenium ion
$b)$ Partial double bond character of $C-X$ bond
$c)$ Longer $C-X$ bond
$d)$ $sp^2$ carbon bonded to $X$ is more electronegative

Which of the following does not give Friedel-Crafts reaction?

In which of the following is the $C-Cl$ bond length minimum?