Chlorine exhibits -I effect, pulling electrons towards itself, thus creating a slight positive charge on the carbon attached.
In compound 2, -I effect of chlorine is most pronounced making the compound reactive towards SN2 reaction.
In compound 3, -I effect of chlorine is strong but is countered by the resonance effect making substitution possible at o−,p - positions.
In compound 1, -I effect of chlorine is balanced by the +I effect of the cycloalkyl group.