Question

Arrange the following in decreasing order of their pK$_b$ values:

• A. $d>a>c>b$
• B. $a>b>d>c$
• C. $d>c>b>a$
• D. $a>c>e>b$

Hint:

More delocalization or electron withdrawing groups reduce basicity and thus lower the pK$_b$ value.

Answer 1

The Correct Option is C

Higher pK$_b$ implies weaker base. Lower pK$_b$ implies stronger base.
% Option (d) Aniline with N–CH$_3$ — lone pair less delocalized than in aniline.
% Option (c) Pyridine — basic but N is sp$^2$ hybridized, less basic than sp$^3$.
% Option (b) Methylamine — primary amine.
% Option (a) Aniline — lone pair delocalized with ring → least basic.
Thus, decreasing order: $d>c>b>a$