Acidic properties among the listed substances are most pronounced in 1) propanol-1 2) phenol 3) propane 4) water

Let’s analyze these substances:

propane is a saturated hydrocarbon, does not contain an OH group;

water, propan-1-ol and phenol – contain one OH-group;

The O – H bond is much more polar than the CH bond, i.e. the proton from the OH group will be split off more easily, even from CH, which means that propane will have the weakest acidic properties.

The propyl radical in propan-1-ol has a positive inductive effect, i.e. the electron density on the oxygen atom in the OH group will be higher than in water, the OH bond becomes stronger.

The acidic properties of water are expressed due to the high electronegativity of oxygen.

In phenol, the electron density from oxygen is drawn into the conjugated system of the phenyl ring, due to the positive mesomeric effect of the OH group, which means that the OH bond will be weaker, i.e. acidic properties will be most pronounced.

Answer: phenol has the most pronounced acidic properties.