Pyridine is less basic than triethylamine because.

 Pyridine is less basic than triethylamine because nitrogen in pyridine is ${\mathrm{sp}}^2$ hybridized. The ${\mathrm{sp}}^2$ nitrogen is more electronegative than the ${\mathrm{sp}}^3$ nitrogen. Thus, the tendency of nitrogen to attract electrons is more which reduces its electron-donating nature to foreign species. Therefore, pyridine is less basic than triethylamine.