Three heterocyclic amines are shown below I = pyridine, II = pyrimidine, III = imidazole. What is the order of increasing basicity? (weaker base < stronger base)

Pyrimidine < pyridine < Imidazole.

imidazole is about 100 times more basic than pyridine. The increased basicity results from resonance stabilization of the charge to both nitrogen atoms.

pyrimidine is less basic than pyridine due to the inductive effect of nitrogen that cause uneven distribution of electron