Which of the following is the least basic amine?

p-Aminobenzonitrile p-Nitroaniline p-Chloroaniline p-Bromoaniline

p-Nitroaniline

All the compounds can be considered as aniline with an electron deactivating (withdrawing) group substituted at the para position to NH2. Since nitro group is the most deactivating group compared to halogen and cyanide, p-nitroaniline is the least basic compound.