Why does benzene undergo electrophilic substitution reactions easily and nucleophilic substitutions with difficulty?

Answer

Benzene has high electron density due to the presence of three `pi-"electron pairs "(6pi-" electrons")` above and below the plane of the ring representing double bond. Due to the rich source of electrons `("delocalized "pi-"electrons")`, benzene attreacts the electrophle (slectron-deficient) reagents towards it and repels nuclephile (electron-rich) reagents. Therefore, benzene undergoes electrophilic substitution reactions easily and nuclephilic substituions with difficulty.