Which compound among the following is most reactive towards electrophilic reagents?

The activating groups increase the aromatic electrophilic substitution reaction and deactivating groups decrease the aromatic electrophilic substitution reaction. The $-\mathrm{OH}$ group is more activating group than the $-\mathrm{OR}$ and $-{\mathrm{NHCOCH}}_3$ group.

Hence, the  is most reactive towards electrophilic reagents.