A group that deactivates the benzene ring towards electrophilic substitution but which directs the incoming group principally to the o- and p-position is.

1. -NH₂                   
2. -Cl
3. -NO₂                   
4. -C₂H₅

Which one of the following is most reactive towards electrophillic attack?

(a) 

(b) 

(c) 

(d) 

The presence of a halogen on the benzene ring in a nitration reaction leads to: