Final answer:
Phenol is the most acidic compound among the options because its phenoxide anion gets stabilized by resonance in the aromatic ring, making it easier for the molecule to lose a hydrogen ion.
Step-by-step explanation:
The most acidic compound among the given options is phenol. Phenols, represented as ArOH, where 'Ar' stands for an aromatic ring, are more acidic than alcohols because of the resonance stabilization of their anion. In phenol, the negative charge resulting from loss of a proton (H+) delocalizes over the aromatic structure, which makes it easier for phenol to lose a hydrogen ion and behave as an acid.
Moreover, the phenol molecule consists of an -OH group bound to an sp²-hybridized carbon of a benzene ring. This configuration contributes to the compound's acidic character, as the sp²-hybridized carbon creates a more electronegative environment that supports the release of a hydrogen ion. Phenols are able to react with bases like sodium hydroxide (NaOH) to form salts, displaying their acidic nature, as shown in the reaction: ArOH(aq) + NaOH(aq) → ArONa (aq) + H₂O. The slight acidity of phenol, compared to stronger acids like carboxylic acids, is due to the less effective charge delocalization in phenols as the negative charge is shared by less electronegative carbon atoms compared to the more electronegative oxygen atoms in carboxylic acids.