Which is the most polar substance- benzyl alcohol, benzaldehyde, benzyl acetate, aniline, n, n-dimethylaniline, benzoic acid, naphthalene, benzophenone, biphenyl

benzyl alcohol  

Explanation:

In the following table we can see the polarity of the substances

Substance                    Polarity  

benzyl alcohol              0.608 (relative) - 6.29 in MPa^0.5            

benzaldehyde              non-polar

benzyl acetate             4.32 in MPa^0.5

aniline                           0.420 (relative)

N,N-dimethylaniline     0.179 (relative)

benzoic acid                 non-polar

naphthalene                 non-polar

Benzophenone            non-polar

biphenyl                        non-polar

As can be seen,  benzyl alcohol has the greatest relative polarity and its polarity is greater than benzyl acetate measured in MPa^0.5. Therefore, it is the most polar substance of the list