Pyridinium hydrochloride is a salt of weak base and strong acid. Therefore, pH = 7 − $\frac{1}{2}$ (log X + $\mathrm{p}K_{\mathrm{b}}$) where $\mathrm{K}_{\mathrm{b}}$ = dissociation constant of pyridine 3.44 = 7 - $\frac{1}{2}$ (log 0.02 + $\mathrm{p}K_{\mathrm{b}}$) - 3.56 = $-\frac{1}{2}(-1.70+\mathrm{p}K_{\mathrm{b}})$ ⇒ - 7.12 = 1.0 - $\mathrm{p}K_{\mathrm{b}}$ $\mathrm{p}K_{\mathrm{b}}$ = 1.70 + 7.12 = 8.82, $\mathrm{K}_{\mathrm{b}}$ = antilog (– 8.82) = 1.513 × $10^{-9}$