Which of the following has the highest `PK_(a)` ?

Options

A.
B.
C.
D.

Answer

B

Explanation

Basicity of an aromatic amine `(ArNH_(2))` is decided by the stability of the anilinium ion The more stable the ion the strongger the base i. e higher the `pK_(a)` Electron release tends to disperse the positive charge of the anilinium ion and thus stabilizes the ion relative to the amine Electron withdrawal tends to intensify the positive charge of the anilinium ion and thus destabilizes the ion relative to mine Thus an electron releasing substituent like `-CH_(3)` increases the basicity of aniline while an electron withdrawing substituent like `-X` or `-NO_(2)` decreases the basicity Since `-NO_(2)` is more electron withdrawing relative to `-X` the correct order of basicity is