Benzene is a planar molecule having delocalized electrons above and below the plane of its ring. Hence, it is an electron-rich species, due to which it is highly attractive to electron deficient

species i.e., electrophiles.

Therefore, it undergoes electrophilic substitution reactions very easily.

Nucleophiles are electron-rich species. Hence, they are repelled by benzene(an electron-rich species). Hence, benzene undergoes nucleophilic substitutions with difficulty.