Question

why does haloarenes less reactive than haloalkanes towards nucleophilic substitution reaction

Answer 1

may this answer help u

Answer 2

There are various reasons for haloarenes being the less reactive than the haloalkanes towards nucleophilic substitution 

1) haloarenes are more stabilize due to having more resonance stability.
2)Also the hybridization in haloarenes is sp2 as compared to the sp3 in the  haloalkanes due to which bond become more stronger between C-X bond in the haloarenes resulting in more difficulty of the nucleophilic substitution.This is because sp2 have more electronegativity

Hope this will help you to understand.