Which molecules are most polar?

Hello! Polarity decreases in this way:

Water > Methanol > Ethanol > 1-propanol > 2-propanol > 1-butanol > acetone.

This trend can be explained by several factors. The presence of hydroxyl groups, -OH, increases the polarity of the molecule. Hydroxyl groups are more polar than carbonyl groups, C=O; hence, alcohols are generally more polar than ketones like acetone. Molecules with terminal hydroxyl groups are more polar than their counterparts that possess internal hydroxyl groups. This is because the hydroxyl groups are less hindered and more exposed to interact and form dipole-dipole interactions. Also, the longer the carbon chain, the less the polarity of the molecule.

I hope this helps! God bless! :)