Question

Alkyl halide take part in nucleophilic substitution reaction but aryl halide cannot explain

Answer 1

Alkyl halides can take part in nucleophilic substitution reactions but Aryl halides cannot and it is due to the partial double bond character between carbon and the halide.

The partial double bond is due to the lone pair present on the halide.

Now u may ask why it doesn't happen in alkyl halides, but actually partial double bond happens to form when the halide donates its lone pair to form a double bond. But why does it donate its lone pair?
well, it is because of conjugation, which occurs when a double bond is in an alternate position to a lone pair.

In the case of Aryl halides, one of the double bonds of the benzene ring is in alternate position to the lone pair which tends the halide to donate its lone pair.
Why does it happen anyway? 
Conjugation happens to gain stability. 

Now coming to your question, this partial double bond character increases the bond strength and does not let nucleophilic substitution of halide to happen in case of Aryl halides.