Which of the following is an example of electrophilic substitution?

 In diazo coupling, ${\mathrm{ArN}}_2\mathrm{Cl}$ reacts with phenol to form a diazo coupling product. The ${\mathrm{ArN}}_2\mathrm{Cl}$ acts as an electrophile and the $\mathrm{OH}$ group in phenol is an electron donating group so it favors the electrophilic substitution reaction. Hence, the diazo coupling reaction is an example of electrophilic substitution.