As a result, the availability of the unshared pair of electrons on nitrogen atom in p - nitroaniline is highly reduced as compared to the unshared electron pair on nitrogen in aniline. ...

Is p-nitroaniline a strong base?

Secondly, aniline and p-nitroaniline (first two green shaded structures) are weaker bases due to delocalization of the nitrogen non-bonding electron pair into the aromatic ring (and the nitro substituent).

Why p-nitroaniline is weaker base than M nitroaniline?

In the o-nitroaniline and p-nitroaniline compound, delocalization of the lone pair is observed. ... Therefore, o-nitroaniline is less basic than p-nitroaniline compounds. In m-nitroaniline only inductive effect is observed and therefore, it is more basic compared to others.