Aniline (Kb4-2 x 10-10) is less basic than ethyl amine (Kb5.1 x 10-4).
This is because -I effect of phenyl group in aniline as compared to + 1 effect of ethyl group in ethyl amine.
Due to resonance,
The lone pair of electrons on the nitrogen atom gets delocalized over the benzene ring and thus less available for protonation.
On the other hand, in ethyl anine,
Delocalization of the lone pair of electrons on the nitrogen atom by resonance is not possible.
Further more,
The electron density on the nitrogen atom is increased by +1 effect of the ethyl group.
Hence,
Aniline is less basic than ethyl amine.
