pyridine is more basic than aniline and acetic acid is more acidic than methanol .

Why is pyridine more basic than aniline?

The strength of basicity depends on the tendency to donate an electron to the electron deficient element, ion or group. 
In case of aniline, the lone pair of electrons on nitrogen atom takes part in the resonance with the pi electron of benzene ring.

As a result, the availability of electrons for donation  is not easy which decrease the tendency to donate electron and hence basicity of aniline decreases.

On the other hand, in case of pyridine the lone of electron on nitrogen atom does not participate in the resonance with the pi electron of pyridine ring . 
Because, the p-orbital of carbon atom is mutually perpendicular to the p-orbital of nitrogen atom.

Therefor, the resonance between p-orbital of carbon atom and p-orbital of nitrogen atom does not occur. 

Hence ,the lone pair of electron on ‘N’-atom is available for donation to the electron deficient element, ion or group.Consequently, pyridine is more basic than aniline.

Why is acetic acid more acidic than methanol?

If acetic acid is ionized in aqueous solution, it gives H⁺ cation and acetate anion. On the other hand, on ionization, methanol gives H⁺cation and methoxide anion.

Now, the strength of acid depends on the relative stability of their concerned anion ( that is conjugate base ). Acetate anion have two equivalent resonating  structure through which it is stabilized. 

But methoxide anion have no such type of resonating structure. In addition to, +I effect of methyl group destabilized the methoxide anion.

Consequently, acetic acid becomes more acidic than methanol.

Why phenols are more acidic than ethanol?

Phenols are more acidic than ethanol. This can be explained by the resonating structure of phenol.The lone pair on oxygen atom takes part  in resonance with the pi electron of benzene ring .

As a result, the oxygen atom of phenol getspartial positive charge . So, the oxygen atom attract the O – H  bonded electron towards itself.

Hence, O – H bond becomes more polar and also more weak . Due to this , the O – H  bond breaks easily to release H⁺ ion.

But in case of ethanol,there is no conjugation . Hence, such type of resonance is not possible

Therefore , the O – H bond of ethanol is more stronger than phenol and hence the tendency to release proton is very much less .Consequently, phenol is more acidic than ethanol.

 Summary

Why is pyridine more basic than aniline ?

Why is acetic acid more acidic than methanol ?

Why phenols are more acidic than ethanol ?

Phenol is acidic or basic