(a)
During nitration benzene ring is attacked by $NO_{2}^{+}$ and hydrogen of benzene ring is replaced by $NO_{2}$ group.
$\therefore$ Nitration of benzene is electrophilic substitution because $NO_{2}^{+}$ is an electrophile.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.