pKa value is indicative of acid strength. Lower of pKa value stronger the acid. Alcohols, phenols and carboxylic acids, all involve ionization of an O – H bond. But their different pKa values indicate that their acid strengths are different. This is because the resulting conjugate bases are stabilized to different extents.
As the conjugate base of carboxylic acid is best stabilized, among the three, carboxylic acids are strongest and have the lowest pKa value. As conjugate base of alcohols is destabilized, alcohols are weakest acids and have highest pIQ value. As conjugate base of phenols is moderately stabilized, phenols are moderately acidic and have intermediate pBQ value.